From ed40a10431701d683bfd59f7ca01a8c97408cf67 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:31 -0700 Subject: uprobes/x86: Use existing definitions for segment override prefixes Rather than using hard-coded values of the segment override prefixes, leverage the existing definitions provided in inat.h. Suggested-by: Borislav Petkov Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: Srikar Dronamraju Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Paul Gortmaker Cc: Huang Rui Cc: Shuah Khan Cc: Jonathan Corbet Cc: Jiri Slaby Cc: "Ravi V. Shankar" Cc: Denys Vlasenko Cc: Chris Metcalf Cc: Brian Gerst Cc: Andy Lutomirski Cc: Chen Yucong Cc: Vlastimil Babka Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Link: https://lkml.kernel.org/r/1509135945-13762-5-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/kernel/uprobes.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index 495c776de4b4..a3755d293a48 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -271,12 +271,15 @@ static bool is_prefix_bad(struct insn *insn) int i; for (i = 0; i < insn->prefixes.nbytes; i++) { - switch (insn->prefixes.bytes[i]) { - case 0x26: /* INAT_PFX_ES */ - case 0x2E: /* INAT_PFX_CS */ - case 0x36: /* INAT_PFX_DS */ - case 0x3E: /* INAT_PFX_SS */ - case 0xF0: /* INAT_PFX_LOCK */ + insn_attr_t attr; + + attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]); + switch (attr) { + case INAT_MAKE_PREFIX(INAT_PFX_ES): + case INAT_MAKE_PREFIX(INAT_PFX_CS): + case INAT_MAKE_PREFIX(INAT_PFX_DS): + case INAT_MAKE_PREFIX(INAT_PFX_SS): + case INAT_MAKE_PREFIX(INAT_PFX_LOCK): return true; } } -- cgit v1.2.3 From b15d70df6e685912be8bbcb7557d277d48aa942c Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:32 -0700 Subject: x86/mpx: Simplify handling of errors when computing linear addresses When errors occur in the computation of the linear address, -1L is returned. Rather than having a separate return path for errors, the variable used to return the computed linear address can be initialized with the error value. Hence, only one return path is needed. This makes the function easier to read. While here, ensure that the error value is -1L, a 64-bit value, rather than -1, a 32-bit value. Suggested-by: Borislav Petkov Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: Adan Hawthorn Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Nathan Howard Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Joe Perches Cc: Paolo Bonzini Cc: Andrew Morton Link: https://lkml.kernel.org/r/1509135945-13762-6-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/mm/mpx.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 9ceaa955d2ba..f4c48a01c906 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -138,7 +138,7 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, */ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) { - unsigned long addr, base, indx; + unsigned long addr = -1L, base, indx; int addr_offset, base_offset, indx_offset; insn_byte_t sib; @@ -149,17 +149,17 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) if (X86_MODRM_MOD(insn->modrm.value) == 3) { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); if (addr_offset < 0) - goto out_err; + goto out; addr = regs_get_register(regs, addr_offset); } else { if (insn->sib.nbytes) { base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); if (base_offset < 0) - goto out_err; + goto out; indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); if (indx_offset < 0) - goto out_err; + goto out; base = regs_get_register(regs, base_offset); indx = regs_get_register(regs, indx_offset); @@ -167,14 +167,13 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); if (addr_offset < 0) - goto out_err; + goto out; addr = regs_get_register(regs, addr_offset); } addr += insn->displacement.value; } +out: return (void __user *)addr; -out_err: - return (void __user *)-1; } static int mpx_insn_decode(struct insn *insn, -- cgit v1.2.3 From b8d2eff3b1c6e46238a5fb3f56843e9974b4889f Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:33 -0700 Subject: x86/mpx: Use signed variables to compute effective addresses Even though memory addresses are unsigned, the operands used to compute the effective address do have a sign. This is true for ModRM.rm, SIB.base, SIB.index as well as the displacement bytes. Thus, signed variables shall be used when computing the effective address from these operands. Once the signed effective address has been computed, it is casted to an unsigned long to determine the linear address. Variables are renamed to better reflect the type of address being computed. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: Adan Hawthorn Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Nathan Howard Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Joe Perches Cc: Paolo Bonzini Cc: Andrew Morton Link: https://lkml.kernel.org/r/1509135945-13762-7-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/mm/mpx.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index f4c48a01c906..57e5bf58ea34 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -138,8 +138,9 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, */ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) { - unsigned long addr = -1L, base, indx; int addr_offset, base_offset, indx_offset; + unsigned long linear_addr = -1L; + long eff_addr, base, indx; insn_byte_t sib; insn_get_modrm(insn); @@ -150,7 +151,8 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); if (addr_offset < 0) goto out; - addr = regs_get_register(regs, addr_offset); + + eff_addr = regs_get_register(regs, addr_offset); } else { if (insn->sib.nbytes) { base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); @@ -163,17 +165,23 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) base = regs_get_register(regs, base_offset); indx = regs_get_register(regs, indx_offset); - addr = base + indx * (1 << X86_SIB_SCALE(sib)); + + eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); if (addr_offset < 0) goto out; - addr = regs_get_register(regs, addr_offset); + + eff_addr = regs_get_register(regs, addr_offset); } - addr += insn->displacement.value; + + eff_addr += insn->displacement.value; } + + linear_addr = (unsigned long)eff_addr; + out: - return (void __user *)addr; + return (void __user *)linear_addr; } static int mpx_insn_decode(struct insn *insn, -- cgit v1.2.3 From ff9d78025c519046cfbc212b34f09116685402fc Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:34 -0700 Subject: x86/mpx: Do not use SIB.index if its value is 100b and ModRM.mod is not 11b Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when ModRM.mod !=11b and ModRM.rm = 100b indexed register-indirect addressing is used. In other words, a SIB byte follows the ModRM byte. In the specific case of SIB.index = 100b, the scale*index portion of the computation of the effective address is null. To signal callers of this particular situation, get_reg_offset() can return -EDOM (-EINVAL continues to indicate that an error when decoding the SIB byte). An example of this situation can be the following instruction: 8b 4c 23 80 mov -0x80(%rbx,%riz,1),%rcx ModRM: 0x4c [mod:1b][reg:1b][rm:100b] SIB: 0x23 [scale:0b][index:100b][base:11b] Displacement: 0x80 (1-byte, as per ModRM.mod = 1b) The %riz 'register' indicates a null index. In long mode, a REX prefix may be used. When a REX prefix is present, REX.X adds a fourth bit to the register selection of SIB.index. This gives the ability to refer to all the 16 general purpose registers. When REX.X is 1b and SIB.index is 100b, the index is indicated in %r12. In our example, this would look like: 42 8b 4c 23 80 mov -0x80(%rbx,%r12,1),%rcx REX: 0x42 [W:0b][R:0b][X:1b][B:0b] ModRM: 0x4c [mod:1b][reg:1b][rm:100b] SIB: 0x23 [scale:0b][.X: 1b, index:100b][.B:0b, base:11b] Displacement: 0x80 (1-byte, as per ModRM.mod = 1b) %r12 is a valid register to use in the scale*index part of the effective address computation. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: Adan Hawthorn Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Nathan Howard Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Joe Perches Cc: Paolo Bonzini Cc: Andrew Morton Link: https://lkml.kernel.org/r/1509135945-13762-8-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/mm/mpx.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 57e5bf58ea34..2ad1d4a42fcc 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -110,6 +110,15 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, regno = X86_SIB_INDEX(insn->sib.value); if (X86_REX_X(insn->rex_prefix.value)) regno += 8; + + /* + * If ModRM.mod != 3 and SIB.index = 4 the scale*index + * portion of the address computation is null. This is + * true only if REX.X is 0. In such a case, the SIB index + * is used in the address computation. + */ + if (X86_MODRM_MOD(insn->modrm.value) != 3 && regno == 4) + return -EDOM; break; case REG_TYPE_BASE: @@ -160,11 +169,19 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) goto out; indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); - if (indx_offset < 0) + /* + * A negative offset generally means a error, except + * -EDOM, which means that the contents of the register + * should not be used as index. + */ + if (indx_offset == -EDOM) + indx = 0; + else if (indx_offset < 0) goto out; + else + indx = regs_get_register(regs, indx_offset); base = regs_get_register(regs, base_offset); - indx = regs_get_register(regs, indx_offset); eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { -- cgit v1.2.3 From 4578f06fc93fb73c9c644ed838f4cdabbfdc4df1 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:35 -0700 Subject: x86/mpx: Do not use SIB.base if its value is 101b and ModRM.mod = 0 Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that if a SIB byte is used and SIB.base is 101b and ModRM.mod is zero, then the base part of the base part of the effective address computation is null. To signal this situation, a -EDOM error is returned to indicate callers to ignore the base value present in the register operand. In this scenario, a 32-bit displacement follows the SIB byte. Displacement is obtained when the instruction decoder parses the operands. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: Adan Hawthorn Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Nathan Howard Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Joe Perches Cc: Paolo Bonzini Cc: Andrew Morton Link: https://lkml.kernel.org/r/1509135945-13762-9-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/mm/mpx.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 2ad1d4a42fcc..581a960a4f09 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -123,6 +123,14 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, case REG_TYPE_BASE: regno = X86_SIB_BASE(insn->sib.value); + /* + * If ModRM.mod is 0 and SIB.base == 5, the base of the + * register-indirect addressing is 0. In this case, a + * 32-bit displacement follows the SIB byte. + */ + if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5) + return -EDOM; + if (X86_REX_B(insn->rex_prefix.value)) regno += 8; break; @@ -164,16 +172,22 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) eff_addr = regs_get_register(regs, addr_offset); } else { if (insn->sib.nbytes) { + /* + * Negative values in the base and index offset means + * an error when decoding the SIB byte. Except -EDOM, + * which means that the registers should not be used + * in the address computation. + */ base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); - if (base_offset < 0) + if (base_offset == -EDOM) + base = 0; + else if (base_offset < 0) goto out; + else + base = regs_get_register(regs, base_offset); indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); - /* - * A negative offset generally means a error, except - * -EDOM, which means that the contents of the register - * should not be used as index. - */ + if (indx_offset == -EDOM) indx = 0; else if (indx_offset < 0) @@ -181,8 +195,6 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) else indx = regs_get_register(regs, indx_offset); - base = regs_get_register(regs, base_offset); - eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); -- cgit v1.2.3 From 32542ee295bec38e5e1608f8c9d6d28e5a7e6112 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:36 -0700 Subject: x86/mpx, x86/insn: Relocate insn util functions to a new insn-eval file Other kernel submodules can benefit from using the utility functions defined in mpx.c to obtain the addresses and values of operands contained in the general purpose registers. An instance of this is the emulation code used for instructions protected by the Intel User-Mode Instruction Prevention feature. Thus, these functions are relocated to a new insn-eval.c file. The reason to not relocate these utilities into insn.c is that the latter solely analyses instructions given by a struct insn without any knowledge of the meaning of the values of instruction operands. This new utility insn- eval.c aims to be used to resolve userspace linear addresses based on the contents of the instruction operands as well as the contents of pt_regs structure. These utilities come with a separate header. This is to avoid taking insn.c out of sync from the instructions decoders under tools/obj and tools/perf. This also avoids adding cumbersome #ifdef's for the #include'd files required to decode instructions in a kernel context. Functions are simply relocated. There are not functional or indentation changes. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-10-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/include/asm/insn-eval.h | 16 ++++ arch/x86/lib/Makefile | 2 +- arch/x86/lib/insn-eval.c | 163 +++++++++++++++++++++++++++++++++++++++ arch/x86/mm/mpx.c | 156 +------------------------------------ 4 files changed, 182 insertions(+), 155 deletions(-) create mode 100644 arch/x86/include/asm/insn-eval.h create mode 100644 arch/x86/lib/insn-eval.c diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h new file mode 100644 index 000000000000..5cab1b1da84d --- /dev/null +++ b/arch/x86/include/asm/insn-eval.h @@ -0,0 +1,16 @@ +#ifndef _ASM_X86_INSN_EVAL_H +#define _ASM_X86_INSN_EVAL_H +/* + * A collection of utility functions for x86 instruction analysis to be + * used in a kernel context. Useful when, for instance, making sense + * of the registers indicated by operands. + */ + +#include +#include +#include +#include + +void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs); + +#endif /* _ASM_X86_INSN_EVAL_H */ diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile index 34a74131a12c..675d7b075fed 100644 --- a/arch/x86/lib/Makefile +++ b/arch/x86/lib/Makefile @@ -23,7 +23,7 @@ lib-y := delay.o misc.o cmdline.o cpu.o lib-y += usercopy_$(BITS).o usercopy.o getuser.o putuser.o lib-y += memcpy_$(BITS).o lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o -lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o +lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o lib-$(CONFIG_RANDOMIZE_BASE) += kaslr.o obj-y += msr.o msr-reg.o msr-reg-export.o hweight.o diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c new file mode 100644 index 000000000000..df9418c43356 --- /dev/null +++ b/arch/x86/lib/insn-eval.c @@ -0,0 +1,163 @@ +/* + * Utility functions for x86 operand and address decoding + * + * Copyright (C) Intel Corporation 2017 + */ +#include +#include +#include +#include +#include + +enum reg_type { + REG_TYPE_RM = 0, + REG_TYPE_INDEX, + REG_TYPE_BASE, +}; + +static int get_reg_offset(struct insn *insn, struct pt_regs *regs, + enum reg_type type) +{ + int regno = 0; + + static const int regoff[] = { + offsetof(struct pt_regs, ax), + offsetof(struct pt_regs, cx), + offsetof(struct pt_regs, dx), + offsetof(struct pt_regs, bx), + offsetof(struct pt_regs, sp), + offsetof(struct pt_regs, bp), + offsetof(struct pt_regs, si), + offsetof(struct pt_regs, di), +#ifdef CONFIG_X86_64 + offsetof(struct pt_regs, r8), + offsetof(struct pt_regs, r9), + offsetof(struct pt_regs, r10), + offsetof(struct pt_regs, r11), + offsetof(struct pt_regs, r12), + offsetof(struct pt_regs, r13), + offsetof(struct pt_regs, r14), + offsetof(struct pt_regs, r15), +#endif + }; + int nr_registers = ARRAY_SIZE(regoff); + /* + * Don't possibly decode a 32-bit instructions as + * reading a 64-bit-only register. + */ + if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64) + nr_registers -= 8; + + switch (type) { + case REG_TYPE_RM: + regno = X86_MODRM_RM(insn->modrm.value); + if (X86_REX_B(insn->rex_prefix.value)) + regno += 8; + break; + + case REG_TYPE_INDEX: + regno = X86_SIB_INDEX(insn->sib.value); + if (X86_REX_X(insn->rex_prefix.value)) + regno += 8; + + /* + * If ModRM.mod != 3 and SIB.index = 4 the scale*index + * portion of the address computation is null. This is + * true only if REX.X is 0. In such a case, the SIB index + * is used in the address computation. + */ + if (X86_MODRM_MOD(insn->modrm.value) != 3 && regno == 4) + return -EDOM; + break; + + case REG_TYPE_BASE: + regno = X86_SIB_BASE(insn->sib.value); + /* + * If ModRM.mod is 0 and SIB.base == 5, the base of the + * register-indirect addressing is 0. In this case, a + * 32-bit displacement follows the SIB byte. + */ + if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5) + return -EDOM; + + if (X86_REX_B(insn->rex_prefix.value)) + regno += 8; + break; + + default: + pr_err("invalid register type"); + BUG(); + break; + } + + if (regno >= nr_registers) { + WARN_ONCE(1, "decoded an instruction with an invalid register"); + return -EINVAL; + } + return regoff[regno]; +} + +/* + * return the address being referenced be instruction + * for rm=3 returning the content of the rm reg + * for rm!=3 calculates the address using SIB and Disp + */ +void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) +{ + int addr_offset, base_offset, indx_offset; + unsigned long linear_addr = -1L; + long eff_addr, base, indx; + insn_byte_t sib; + + insn_get_modrm(insn); + insn_get_sib(insn); + sib = insn->sib.value; + + if (X86_MODRM_MOD(insn->modrm.value) == 3) { + addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); + if (addr_offset < 0) + goto out; + + eff_addr = regs_get_register(regs, addr_offset); + } else { + if (insn->sib.nbytes) { + /* + * Negative values in the base and index offset means + * an error when decoding the SIB byte. Except -EDOM, + * which means that the registers should not be used + * in the address computation. + */ + base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); + if (base_offset == -EDOM) + base = 0; + else if (base_offset < 0) + goto out; + else + base = regs_get_register(regs, base_offset); + + indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); + + if (indx_offset == -EDOM) + indx = 0; + else if (indx_offset < 0) + goto out; + else + indx = regs_get_register(regs, indx_offset); + + eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); + } else { + addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); + if (addr_offset < 0) + goto out; + + eff_addr = regs_get_register(regs, addr_offset); + } + + eff_addr += insn->displacement.value; + } + + linear_addr = (unsigned long)eff_addr; + +out: + return (void __user *)linear_addr; +} diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 581a960a4f09..28782059ad2d 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -12,6 +12,7 @@ #include #include +#include #include #include #include @@ -60,159 +61,6 @@ static unsigned long mpx_mmap(unsigned long len) return addr; } -enum reg_type { - REG_TYPE_RM = 0, - REG_TYPE_INDEX, - REG_TYPE_BASE, -}; - -static int get_reg_offset(struct insn *insn, struct pt_regs *regs, - enum reg_type type) -{ - int regno = 0; - - static const int regoff[] = { - offsetof(struct pt_regs, ax), - offsetof(struct pt_regs, cx), - offsetof(struct pt_regs, dx), - offsetof(struct pt_regs, bx), - offsetof(struct pt_regs, sp), - offsetof(struct pt_regs, bp), - offsetof(struct pt_regs, si), - offsetof(struct pt_regs, di), -#ifdef CONFIG_X86_64 - offsetof(struct pt_regs, r8), - offsetof(struct pt_regs, r9), - offsetof(struct pt_regs, r10), - offsetof(struct pt_regs, r11), - offsetof(struct pt_regs, r12), - offsetof(struct pt_regs, r13), - offsetof(struct pt_regs, r14), - offsetof(struct pt_regs, r15), -#endif - }; - int nr_registers = ARRAY_SIZE(regoff); - /* - * Don't possibly decode a 32-bit instructions as - * reading a 64-bit-only register. - */ - if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64) - nr_registers -= 8; - - switch (type) { - case REG_TYPE_RM: - regno = X86_MODRM_RM(insn->modrm.value); - if (X86_REX_B(insn->rex_prefix.value)) - regno += 8; - break; - - case REG_TYPE_INDEX: - regno = X86_SIB_INDEX(insn->sib.value); - if (X86_REX_X(insn->rex_prefix.value)) - regno += 8; - - /* - * If ModRM.mod != 3 and SIB.index = 4 the scale*index - * portion of the address computation is null. This is - * true only if REX.X is 0. In such a case, the SIB index - * is used in the address computation. - */ - if (X86_MODRM_MOD(insn->modrm.value) != 3 && regno == 4) - return -EDOM; - break; - - case REG_TYPE_BASE: - regno = X86_SIB_BASE(insn->sib.value); - /* - * If ModRM.mod is 0 and SIB.base == 5, the base of the - * register-indirect addressing is 0. In this case, a - * 32-bit displacement follows the SIB byte. - */ - if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5) - return -EDOM; - - if (X86_REX_B(insn->rex_prefix.value)) - regno += 8; - break; - - default: - pr_err("invalid register type"); - BUG(); - break; - } - - if (regno >= nr_registers) { - WARN_ONCE(1, "decoded an instruction with an invalid register"); - return -EINVAL; - } - return regoff[regno]; -} - -/* - * return the address being referenced be instruction - * for rm=3 returning the content of the rm reg - * for rm!=3 calculates the address using SIB and Disp - */ -static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) -{ - int addr_offset, base_offset, indx_offset; - unsigned long linear_addr = -1L; - long eff_addr, base, indx; - insn_byte_t sib; - - insn_get_modrm(insn); - insn_get_sib(insn); - sib = insn->sib.value; - - if (X86_MODRM_MOD(insn->modrm.value) == 3) { - addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); - if (addr_offset < 0) - goto out; - - eff_addr = regs_get_register(regs, addr_offset); - } else { - if (insn->sib.nbytes) { - /* - * Negative values in the base and index offset means - * an error when decoding the SIB byte. Except -EDOM, - * which means that the registers should not be used - * in the address computation. - */ - base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); - if (base_offset == -EDOM) - base = 0; - else if (base_offset < 0) - goto out; - else - base = regs_get_register(regs, base_offset); - - indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); - - if (indx_offset == -EDOM) - indx = 0; - else if (indx_offset < 0) - goto out; - else - indx = regs_get_register(regs, indx_offset); - - eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); - } else { - addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); - if (addr_offset < 0) - goto out; - - eff_addr = regs_get_register(regs, addr_offset); - } - - eff_addr += insn->displacement.value; - } - - linear_addr = (unsigned long)eff_addr; - -out: - return (void __user *)linear_addr; -} - static int mpx_insn_decode(struct insn *insn, struct pt_regs *regs) { @@ -325,7 +173,7 @@ siginfo_t *mpx_generate_siginfo(struct pt_regs *regs) info->si_signo = SIGSEGV; info->si_errno = 0; info->si_code = SEGV_BNDERR; - info->si_addr = mpx_get_addr_ref(&insn, regs); + info->si_addr = insn_get_addr_ref(&insn, regs); /* * We were not able to extract an address from the instruction, * probably because there was something invalid in it. -- cgit v1.2.3 From ed594e4ba5bfe268d63d7cee3c1a827e3dd5056f Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:37 -0700 Subject: x86/insn-eval: Do not BUG on invalid register type We are not in a critical failure path. The invalid register type is caused when trying to decode invalid instruction bytes from a user-space program. Thus, simply print an error message. To prevent this warning from being abused from user space programs, use the rate-limited variant of pr_err(). along with a descriptive prefix. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-11-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/lib/insn-eval.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index df9418c43356..4931d9252dde 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -5,10 +5,14 @@ */ #include #include +#include #include #include #include +#undef pr_fmt +#define pr_fmt(fmt) "insn: " fmt + enum reg_type { REG_TYPE_RM = 0, REG_TYPE_INDEX, @@ -85,9 +89,8 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, break; default: - pr_err("invalid register type"); - BUG(); - break; + pr_err_ratelimited("invalid register type: %d\n", type); + return -EINVAL; } if (regno >= nr_registers) { -- cgit v1.2.3 From e5e45f11110191740ecb365fa8c7a25814ce8ac8 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:38 -0700 Subject: x86/insn-eval: Add a utility function to get register offsets The function get_reg_offset() returns the offset to the register the argument specifies as indicated in an enumeration of type offset. Callers of this function would need the definition of such enumeration. This is not needed. Instead, add helper functions for this purpose. These functions are useful in cases when, for instance, the caller needs to decide whether the operand is a register or a memory location by looking at the rm part of the ModRM byte. As of now, this is the only helper function that is needed. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-12-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/include/asm/insn-eval.h | 1 + arch/x86/lib/insn-eval.c | 17 +++++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h index 5cab1b1da84d..7e8c9633a377 100644 --- a/arch/x86/include/asm/insn-eval.h +++ b/arch/x86/include/asm/insn-eval.h @@ -12,5 +12,6 @@ #include void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs); +int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs); #endif /* _ASM_X86_INSN_EVAL_H */ diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 4931d9252dde..405ffeb1c382 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -100,6 +100,23 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, return regoff[regno]; } +/** + * insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte + * @insn: Instruction containing the ModRM byte + * @regs: Register values as seen when entering kernel mode + * + * Returns: + * + * The register indicated by the r/m part of the ModRM byte. The + * register is obtained as an offset from the base of pt_regs. In specific + * cases, the returned value can be -EDOM to indicate that the particular value + * of ModRM does not refer to a register and shall be ignored. + */ +int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs) +{ + return get_reg_offset(insn, regs, REG_TYPE_RM); +} + /* * return the address being referenced be instruction * for rm=3 returning the content of the rm reg -- cgit v1.2.3 From 536b815388f7f4d2a7cd1418939902fb037ea370 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:39 -0700 Subject: x86/insn-eval: Add utility function to identify string instructions String instructions are special because, in protected mode, the linear address is always obtained via the ES segment register in operands that use the (E)DI register; the DS segment register in operands that use the (E)SI register. Furthermore, segment override prefixes are ignored when calculating a linear address involving the (E)DI register; segment override prefixes can be used when calculating linear addresses involving the (E)SI register. It follows that linear addresses are calculated differently for the case of string instructions. The purpose of this utility function is to identify such instructions for callers to determine a linear address correctly. Note that this function only identifies string instructions; it does not determine what segment register to use in the address computation. That is left to callers. A subsequent commmit introduces a function to determine the segment register to use given the instruction, operands and segment override prefixes. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-13-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/lib/insn-eval.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 405ffeb1c382..ac7b87c228b9 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -19,6 +19,34 @@ enum reg_type { REG_TYPE_BASE, }; +/** + * is_string_insn() - Determine if instruction is a string instruction + * @insn: Instruction containing the opcode to inspect + * + * Returns: + * + * true if the instruction, determined by the opcode, is any of the + * string instructions as defined in the Intel Software Development manual. + * False otherwise. + */ +static bool is_string_insn(struct insn *insn) +{ + insn_get_opcode(insn); + + /* All string instructions have a 1-byte opcode. */ + if (insn->opcode.nbytes != 1) + return false; + + switch (insn->opcode.bytes[0]) { + case 0x6c ... 0x6f: /* INS, OUTS */ + case 0xa4 ... 0xa7: /* MOVS, CMPS */ + case 0xaa ... 0xaf: /* STOS, LODS, SCAS */ + return true; + default: + return false; + } +} + static int get_reg_offset(struct insn *insn, struct pt_regs *regs, enum reg_type type) { -- cgit v1.2.3 From 32d0b95300db03c2b23b2ea2c94769a4a138e79d Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:40 -0700 Subject: x86/insn-eval: Add utility functions to get segment selector When computing a linear address and segmentation is used, we need to know the base address of the segment involved in the computation. In most of the cases, the segment base address will be zero as in USER_DS/USER32_DS. However, it may be possible that a user space program defines its own segments via a local descriptor table. In such a case, the segment base address may not be zero. Thus, the segment base address is needed to calculate correctly the linear address. If running in protected mode, the segment selector to be used when computing a linear address is determined by either any of segment override prefixes in the instruction or inferred from the registers involved in the computation of the effective address; in that order. Also, there are cases when the segment override prefixes shall be ignored (i.e., code segments are always selected by the CS segment register; string instructions always use the ES segment register when using rDI register as operand). In long mode, segment registers are ignored, except for FS and GS. In these two cases, base addresses are obtained from the respective MSRs. For clarity, this process can be split into four steps (and an equal number of functions): determine if segment prefixes overrides can be used; parse the segment override prefixes, and use them if found; if not found or cannot be used, use the default segment registers associated with the operand registers. Once the segment register to use has been identified, read its value to obtain the segment selector. The method to obtain the segment selector depends on several factors. In 32-bit builds, segment selectors are saved into a pt_regs structure when switching to kernel mode. The same is also true for virtual-8086 mode. In 64-bit builds, segmentation is mostly ignored, except when running a program in 32-bit legacy mode. In this case, CS and SS can be obtained from pt_regs. DS, ES, FS and GS can be read directly from the respective segment registers. In order to identify the segment registers, a new set of #defines is introduced. It also includes two special identifiers. One of them indicates when the default segment register associated with instruction operands shall be used. Another one indicates that the contents of the segment register shall be ignored; this identifier is used when in long mode. Improvements-by: Borislav Petkov Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-14-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/include/asm/inat.h | 10 ++ arch/x86/lib/insn-eval.c | 340 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 350 insertions(+) diff --git a/arch/x86/include/asm/inat.h b/arch/x86/include/asm/inat.h index 02aff0867211..1c78580e58be 100644 --- a/arch/x86/include/asm/inat.h +++ b/arch/x86/include/asm/inat.h @@ -97,6 +97,16 @@ #define INAT_MAKE_GROUP(grp) ((grp << INAT_GRP_OFFS) | INAT_MODRM) #define INAT_MAKE_IMM(imm) (imm << INAT_IMM_OFFS) +/* Identifiers for segment registers */ +#define INAT_SEG_REG_IGNORE 0 +#define INAT_SEG_REG_DEFAULT 1 +#define INAT_SEG_REG_CS 2 +#define INAT_SEG_REG_SS 3 +#define INAT_SEG_REG_DS 4 +#define INAT_SEG_REG_ES 5 +#define INAT_SEG_REG_FS 6 +#define INAT_SEG_REG_GS 7 + /* Attribute search APIs */ extern insn_attr_t inat_get_opcode_attribute(insn_byte_t opcode); extern int inat_get_last_prefix_id(insn_byte_t last_pfx); diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index ac7b87c228b9..6a902b155f5d 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -9,6 +9,7 @@ #include #include #include +#include #undef pr_fmt #define pr_fmt(fmt) "insn: " fmt @@ -47,6 +48,345 @@ static bool is_string_insn(struct insn *insn) } } +/** + * get_seg_reg_override_idx() - obtain segment register override index + * @insn: Valid instruction with segment override prefixes + * + * Inspect the instruction prefixes in @insn and find segment overrides, if any. + * + * Returns: + * + * A constant identifying the segment register to use, among CS, SS, DS, + * ES, FS, or GS. INAT_SEG_REG_DEFAULT is returned if no segment override + * prefixes were found. + * + * -EINVAL in case of error. + */ +static int get_seg_reg_override_idx(struct insn *insn) +{ + int idx = INAT_SEG_REG_DEFAULT; + int num_overrides = 0, i; + + insn_get_prefixes(insn); + + /* Look for any segment override prefixes. */ + for (i = 0; i < insn->prefixes.nbytes; i++) { + insn_attr_t attr; + + attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]); + switch (attr) { + case INAT_MAKE_PREFIX(INAT_PFX_CS): + idx = INAT_SEG_REG_CS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_SS): + idx = INAT_SEG_REG_SS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_DS): + idx = INAT_SEG_REG_DS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_ES): + idx = INAT_SEG_REG_ES; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_FS): + idx = INAT_SEG_REG_FS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_GS): + idx = INAT_SEG_REG_GS; + num_overrides++; + break; + /* No default action needed. */ + } + } + + /* More than one segment override prefix leads to undefined behavior. */ + if (num_overrides > 1) + return -EINVAL; + + return idx; +} + +/** + * check_seg_overrides() - check if segment override prefixes are allowed + * @insn: Valid instruction with segment override prefixes + * @regoff: Operand offset, in pt_regs, for which the check is performed + * + * For a particular register used in register-indirect addressing, determine if + * segment override prefixes can be used. Specifically, no overrides are allowed + * for rDI if used with a string instruction. + * + * Returns: + * + * True if segment override prefixes can be used with the register indicated + * in @regoff. False if otherwise. + */ +static bool check_seg_overrides(struct insn *insn, int regoff) +{ + if (regoff == offsetof(struct pt_regs, di) && is_string_insn(insn)) + return false; + + return true; +} + +/** + * resolve_default_seg() - resolve default segment register index for an operand + * @insn: Instruction with opcode and address size. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @off: Operand offset, in pt_regs, for which resolution is needed + * + * Resolve the default segment register index associated with the instruction + * operand register indicated by @off. Such index is resolved based on defaults + * described in the Intel Software Development Manual. + * + * Returns: + * + * If in protected mode, a constant identifying the segment register to use, + * among CS, SS, ES or DS. If in long mode, INAT_SEG_REG_IGNORE. + * + * -EINVAL in case of error. + */ +static int resolve_default_seg(struct insn *insn, struct pt_regs *regs, int off) +{ + if (user_64bit_mode(regs)) + return INAT_SEG_REG_IGNORE; + /* + * Resolve the default segment register as described in Section 3.7.4 + * of the Intel Software Development Manual Vol. 1: + * + * + DS for all references involving r[ABCD]X, and rSI. + * + If used in a string instruction, ES for rDI. Otherwise, DS. + * + AX, CX and DX are not valid register operands in 16-bit address + * encodings but are valid for 32-bit and 64-bit encodings. + * + -EDOM is reserved to identify for cases in which no register + * is used (i.e., displacement-only addressing). Use DS. + * + SS for rSP or rBP. + * + CS for rIP. + */ + + switch (off) { + case offsetof(struct pt_regs, ax): + case offsetof(struct pt_regs, cx): + case offsetof(struct pt_regs, dx): + /* Need insn to verify address size. */ + if (insn->addr_bytes == 2) + return -EINVAL; + + case -EDOM: + case offsetof(struct pt_regs, bx): + case offsetof(struct pt_regs, si): + return INAT_SEG_REG_DS; + + case offsetof(struct pt_regs, di): + if (is_string_insn(insn)) + return INAT_SEG_REG_ES; + return INAT_SEG_REG_DS; + + case offsetof(struct pt_regs, bp): + case offsetof(struct pt_regs, sp): + return INAT_SEG_REG_SS; + + case offsetof(struct pt_regs, ip): + return INAT_SEG_REG_CS; + + default: + return -EINVAL; + } +} + +/** + * resolve_seg_reg() - obtain segment register index + * @insn: Instruction with operands + * @regs: Register values as seen when entering kernel mode + * @regoff: Operand offset, in pt_regs, used to deterimine segment register + * + * Determine the segment register associated with the operands and, if + * applicable, prefixes and the instruction pointed by @insn. + * + * The segment register associated to an operand used in register-indirect + * addressing depends on: + * + * a) Whether running in long mode (in such a case segments are ignored, except + * if FS or GS are used). + * + * b) Whether segment override prefixes can be used. Certain instructions and + * registers do not allow override prefixes. + * + * c) Whether segment overrides prefixes are found in the instruction prefixes. + * + * d) If there are not segment override prefixes or they cannot be used, the + * default segment register associated with the operand register is used. + * + * The function checks first if segment override prefixes can be used with the + * operand indicated by @regoff. If allowed, obtain such overridden segment + * register index. Lastly, if not prefixes were found or cannot be used, resolve + * the segment register index to use based on the defaults described in the + * Intel documentation. In long mode, all segment register indexes will be + * ignored, except if overrides were found for FS or GS. All these operations + * are done using helper functions. + * + * The operand register, @regoff, is represented as the offset from the base of + * pt_regs. + * + * As stated, the main use of this function is to determine the segment register + * index based on the instruction, its operands and prefixes. Hence, @insn + * must be valid. However, if @regoff indicates rIP, we don't need to inspect + * @insn at all as in this case CS is used in all cases. This case is checked + * before proceeding further. + * + * Please note that this function does not return the value in the segment + * register (i.e., the segment selector) but our defined index. The segment + * selector needs to be obtained using get_segment_selector() and passing the + * segment register index resolved by this function. + * + * Returns: + * + * An index identifying the segment register to use, among CS, SS, DS, + * ES, FS, or GS. INAT_SEG_REG_IGNORE is returned if running in long mode. + * + * -EINVAL in case of error. + */ +static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff) +{ + int idx; + + /* + * In the unlikely event of having to resolve the segment register + * index for rIP, do it first. Segment override prefixes should not + * be used. Hence, it is not necessary to inspect the instruction, + * which may be invalid at this point. + */ + if (regoff == offsetof(struct pt_regs, ip)) { + if (user_64bit_mode(regs)) + return INAT_SEG_REG_IGNORE; + else + return INAT_SEG_REG_CS; + } + + if (!insn) + return -EINVAL; + + if (!check_seg_overrides(insn, regoff)) + return resolve_default_seg(insn, regs, regoff); + + idx = get_seg_reg_override_idx(insn); + if (idx < 0) + return idx; + + if (idx == INAT_SEG_REG_DEFAULT) + return resolve_default_seg(insn, regs, regoff); + + /* + * In long mode, segment override prefixes are ignored, except for + * overrides for FS and GS. + */ + if (user_64bit_mode(regs)) { + if (idx != INAT_SEG_REG_FS && + idx != INAT_SEG_REG_GS) + idx = INAT_SEG_REG_IGNORE; + } + + return idx; +} + +/** + * get_segment_selector() - obtain segment selector + * @regs: Register values as seen when entering kernel mode + * @seg_reg_idx: Segment register index to use + * + * Obtain the segment selector from any of the CS, SS, DS, ES, FS, GS segment + * registers. In CONFIG_X86_32, the segment is obtained from either pt_regs or + * kernel_vm86_regs as applicable. In CONFIG_X86_64, CS and SS are obtained + * from pt_regs. DS, ES, FS and GS are obtained by reading the actual CPU + * registers. This done for only for completeness as in CONFIG_X86_64 segment + * registers are ignored. + * + * Returns: + * + * Value of the segment selector, including null when running in + * long mode. + * + * -EINVAL on error. + */ +static short get_segment_selector(struct pt_regs *regs, int seg_reg_idx) +{ +#ifdef CONFIG_X86_64 + unsigned short sel; + + switch (seg_reg_idx) { + case INAT_SEG_REG_IGNORE: + return 0; + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + savesegment(ds, sel); + return sel; + case INAT_SEG_REG_ES: + savesegment(es, sel); + return sel; + case INAT_SEG_REG_FS: + savesegment(fs, sel); + return sel; + case INAT_SEG_REG_GS: + savesegment(gs, sel); + return sel; + default: + return -EINVAL; + } +#else /* CONFIG_X86_32 */ + struct kernel_vm86_regs *vm86regs = (struct kernel_vm86_regs *)regs; + + if (v8086_mode(regs)) { + switch (seg_reg_idx) { + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + return vm86regs->ds; + case INAT_SEG_REG_ES: + return vm86regs->es; + case INAT_SEG_REG_FS: + return vm86regs->fs; + case INAT_SEG_REG_GS: + return vm86regs->gs; + case INAT_SEG_REG_IGNORE: + /* fall through */ + default: + return -EINVAL; + } + } + + switch (seg_reg_idx) { + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + return (unsigned short)(regs->ds & 0xffff); + case INAT_SEG_REG_ES: + return (unsigned short)(regs->es & 0xffff); + case INAT_SEG_REG_FS: + return (unsigned short)(regs->fs & 0xffff); + case INAT_SEG_REG_GS: + /* + * GS may or may not be in regs as per CONFIG_X86_32_LAZY_GS. + * The macro below takes care of both cases. + */ + return get_user_gs(regs); + case INAT_SEG_REG_IGNORE: + /* fall through */ + default: + return -EINVAL; + } +#endif /* CONFIG_X86_64 */ +} + static int get_reg_offset(struct insn *insn, struct pt_regs *regs, enum reg_type type) { -- cgit v1.2.3 From 670f928ba09b06712da34a3c44be6c8fa561fb19 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:41 -0700 Subject: x86/insn-eval: Add utility function to get segment descriptor The segment descriptor contains information that is relevant to how linear addresses need to be computed. It contains the default size of addresses as well as the base address of the segment. Thus, given a segment selector, we ought to look at segment descriptor to correctly calculate the linear address. In protected mode, the segment selector might indicate a segment descriptor from either the global descriptor table or a local descriptor table. Both cases are considered in this function. This function is a prerequisite for functions in subsequent commits that will obtain the aforementioned attributes of the segment descriptor. Improvements-by: Borislav Petkov Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-15-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/lib/insn-eval.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 6a902b155f5d..d85e84091ddc 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -6,9 +6,13 @@ #include #include #include +#include +#include +#include #include #include #include +#include #include #undef pr_fmt @@ -468,6 +472,59 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, return regoff[regno]; } +/** + * get_desc() - Obtain pointer to a segment descriptor + * @sel: Segment selector + * + * Given a segment selector, obtain a pointer to the segment descriptor. + * Both global and local descriptor tables are supported. + * + * Returns: + * + * Pointer to segment descriptor on success. + * + * NULL on error. + */ +static struct desc_struct *get_desc(unsigned short sel) +{ + struct desc_ptr gdt_desc = {0, 0}; + unsigned long desc_base; + +#ifdef CONFIG_MODIFY_LDT_SYSCALL + if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT) { + struct desc_struct *desc = NULL; + struct ldt_struct *ldt; + + /* Bits [15:3] contain the index of the desired entry. */ + sel >>= 3; + + mutex_lock(¤t->active_mm->context.lock); + ldt = current->active_mm->context.ldt; + if (ldt && sel < ldt->nr_entries) + desc = &ldt->entries[sel]; + + mutex_unlock(¤t->active_mm->context.lock); + + return desc; + } +#endif + native_store_gdt(&gdt_desc); + + /* + * Segment descriptors have a size of 8 bytes. Thus, the index is + * multiplied by 8 to obtain the memory offset of the desired descriptor + * from the base of the GDT. As bits [15:3] of the segment selector + * contain the index, it can be regarded as multiplied by 8 already. + * All that remains is to clear bits [2:0]. + */ + desc_base = sel & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK); + + if (desc_base > gdt_desc.size) + return NULL; + + return (struct desc_struct *)(gdt_desc.address + desc_base); +} + /** * insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte * @insn: Instruction containing the ModRM byte -- cgit v1.2.3 From bd5a410a5de3a6893eaacc749e706b85506dc908 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:42 -0700 Subject: x86/insn-eval: Add utility functions to get segment descriptor base address and limit With segmentation, the base address of the segment is needed to compute a linear address. This base address is obtained from the applicable segment descriptor. Such segment descriptor is referenced from a segment selector. These new functions obtain the segment base and limit of the segment selector indicated by segment register index given as argument. This index is any of the INAT_SEG_REG_* family of #define's. The logic to obtain the segment selector is wrapped in the function get_segment_selector() with the inputs described above. Once the selector is known, the base address is determined. In protected mode, the selector is used to obtain the segment descriptor and then its base address. In long mode, the segment base address is zero except when FS or GS are used. In virtual-8086 mode, the base address is computed as the value of the segment selector shifted 4 positions to the left. In protected mode, segment limits are enforced. Thus, a function to determine the limit of the segment is added. Segment limits are not enforced in long or virtual-8086. For the latter, addresses are limited to 20 bits; address size will be handled when computing the linear address. Improvements-by: Borislav Petkov Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-16-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/include/asm/insn-eval.h | 1 + arch/x86/lib/insn-eval.c | 114 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 115 insertions(+) diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h index 7e8c9633a377..25d6e44dcbfc 100644 --- a/arch/x86/include/asm/insn-eval.h +++ b/arch/x86/include/asm/insn-eval.h @@ -13,5 +13,6 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs); int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs); +unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx); #endif /* _ASM_X86_INSN_EVAL_H */ diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index d85e84091ddc..89d5c8902f42 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -525,6 +525,120 @@ static struct desc_struct *get_desc(unsigned short sel) return (struct desc_struct *)(gdt_desc.address + desc_base); } +/** + * insn_get_seg_base() - Obtain base address of segment descriptor. + * @regs: Register values as seen when entering kernel mode + * @seg_reg_idx: Index of the segment register pointing to seg descriptor + * + * Obtain the base address of the segment as indicated by the segment descriptor + * pointed by the segment selector. The segment selector is obtained from the + * input segment register index @seg_reg_idx. + * + * Returns: + * + * In protected mode, base address of the segment. Zero in long mode, + * except when FS or GS are used. In virtual-8086 mode, the segment + * selector shifted 4 bits to the right. + * + * -1L in case of error. + */ +unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx) +{ + struct desc_struct *desc; + short sel; + + sel = get_segment_selector(regs, seg_reg_idx); + if (sel < 0) + return -1L; + + if (v8086_mode(regs)) + /* + * Base is simply the segment selector shifted 4 + * bits to the right. + */ + return (unsigned long)(sel << 4); + + if (user_64bit_mode(regs)) { + /* + * Only FS or GS will have a base address, the rest of + * the segments' bases are forced to 0. + */ + unsigned long base; + + if (seg_reg_idx == INAT_SEG_REG_FS) + rdmsrl(MSR_FS_BASE, base); + else if (seg_reg_idx == INAT_SEG_REG_GS) + /* + * swapgs was called at the kernel entry point. Thus, + * MSR_KERNEL_GS_BASE will have the user-space GS base. + */ + rdmsrl(MSR_KERNEL_GS_BASE, base); + else + base = 0; + return base; + } + + /* In protected mode the segment selector cannot be null. */ + if (!sel) + return -1L; + + desc = get_desc(sel); + if (!desc) + return -1L; + + return get_desc_base(desc); +} + +/** + * get_seg_limit() - Obtain the limit of a segment descriptor + * @regs: Register values as seen when entering kernel mode + * @seg_reg_idx: Index of the segment register pointing to seg descriptor + * + * Obtain the limit of the segment as indicated by the segment descriptor + * pointed by the segment selector. The segment selector is obtained from the + * input segment register index @seg_reg_idx. + * + * Returns: + * + * In protected mode, the limit of the segment descriptor in bytes. + * In long mode and virtual-8086 mode, segment limits are not enforced. Thus, + * limit is returned as -1L to imply a limit-less segment. + * + * Zero is returned on error. + */ +static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx) +{ + struct desc_struct *desc; + unsigned long limit; + short sel; + + sel = get_segment_selector(regs, seg_reg_idx); + if (sel < 0) + return 0; + + if (user_64bit_mode(regs) || v8086_mode(regs)) + return -1L; + + if (!sel) + return 0; + + desc = get_desc(sel); + if (!desc) + return 0; + + /* + * If the granularity bit is set, the limit is given in multiples + * of 4096. This also means that the 12 least significant bits are + * not tested when checking the segment limits. In practice, + * this means that the segment ends in (limit << 12) + 0xfff. + */ + limit = get_desc_limit(desc); + if (desc->g) + limit = (limit << 12) + 0xfff; + + return limit; +} + /** * insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte * @insn: Instruction containing the ModRM byte -- cgit v1.2.3 From 4efea85fb56fa1691b79af1eea4c1425660cf4e3 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:43 -0700 Subject: x86/insn-eval: Add function to get default params of code segment Obtain the default values of the address and operand sizes as specified in the D and L bits of the the segment descriptor selected by the register CS. The function can be used for both protected and long modes. For virtual-8086 mode, the default address and operand sizes are always 2 bytes. The returned parameters are encoded in a signed 8-bit data type. Auxiliar macros are provided to encode and decode such values. Improvements-by: Borislav Petkov Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-17-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/include/asm/insn-eval.h | 5 ++++ arch/x86/lib/insn-eval.c | 64 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 69 insertions(+) diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h index 25d6e44dcbfc..e1d3b4ce8a92 100644 --- a/arch/x86/include/asm/insn-eval.h +++ b/arch/x86/include/asm/insn-eval.h @@ -11,8 +11,13 @@ #include #include +#define INSN_CODE_SEG_ADDR_SZ(params) ((params >> 4) & 0xf) +#define INSN_CODE_SEG_OPND_SZ(params) (params & 0xf) +#define INSN_CODE_SEG_PARAMS(oper_sz, addr_sz) (oper_sz | (addr_sz << 4)) + void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs); int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs); unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx); +char insn_get_code_seg_params(struct pt_regs *regs); #endif /* _ASM_X86_INSN_EVAL_H */ diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 89d5c8902f42..01e36bd86a5d 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -639,6 +639,70 @@ static unsigned long get_seg_limit(struct pt_regs *regs, int seg_reg_idx) return limit; } +/** + * insn_get_code_seg_params() - Obtain code segment parameters + * @regs: Structure with register values as seen when entering kernel mode + * + * Obtain address and operand sizes of the code segment. It is obtained from the + * selector contained in the CS register in regs. In protected mode, the default + * address is determined by inspecting the L and D bits of the segment + * descriptor. In virtual-8086 mode, the default is always two bytes for both + * address and operand sizes. + * + * Returns: + * + * A signed 8-bit value containing the default parameters on success. + * + * -EINVAL on error. + */ +char insn_get_code_seg_params(struct pt_regs *regs) +{ + struct desc_struct *desc; + short sel; + + if (v8086_mode(regs)) + /* Address and operand size are both 16-bit. */ + return INSN_CODE_SEG_PARAMS(2, 2); + + sel = get_segment_selector(regs, INAT_SEG_REG_CS); + if (sel < 0) + return sel; + + desc = get_desc(sel); + if (!desc) + return -EINVAL; + + /* + * The most significant byte of the Type field of the segment descriptor + * determines whether a segment contains data or code. If this is a data + * segment, return error. + */ + if (!(desc->type & BIT(3))) + return -EINVAL; + + switch ((desc->l << 1) | desc->d) { + case 0: /* + * Legacy mode. CS.L=0, CS.D=0. Address and operand size are + * both 16-bit. + */ + return INSN_CODE_SEG_PARAMS(2, 2); + case 1: /* + * Legacy mode. CS.L=0, CS.D=1. Address and operand size are + * both 32-bit. + */ + return INSN_CODE_SEG_PARAMS(4, 4); + case 2: /* + * IA-32e 64-bit mode. CS.L=1, CS.D=0. Address size is 64-bit; + * operand size is 32-bit. + */ + return INSN_CODE_SEG_PARAMS(4, 8); + case 3: /* Invalid setting. CS.L=1, CS.D=1 */ + /* fall through */ + default: + return -EINVAL; + } +} + /** * insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte * @insn: Instruction containing the ModRM byte -- cgit v1.2.3 From e526a302e425ab11111efc5f59e52449bbcc768e Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:44 -0700 Subject: x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 101b Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when ModRM.mod is zero and ModRM.rm is 101b, a 32-bit displacement follows the ModRM byte. This means that none of the registers are used in the computation of the effective address. A return value of -EDOM indicates callers that they should not use the value of registers when computing the effective address for the instruction. In long mode, the effective address is given by the 32-bit displacement plus the location of the next instruction. In protected mode, only the displacement is used. The instruction decoder takes care of obtaining the displacement. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-18-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/lib/insn-eval.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 01e36bd86a5d..6bf819f923e7 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -427,6 +427,14 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, switch (type) { case REG_TYPE_RM: regno = X86_MODRM_RM(insn->modrm.value); + + /* + * ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit displacement + * follows the ModRM byte. + */ + if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5) + return -EDOM; + if (X86_REX_B(insn->rex_prefix.value)) regno += 8; break; @@ -770,10 +778,21 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); - if (addr_offset < 0) + /* + * -EDOM means that we must ignore the address_offset. + * In such a case, in 64-bit mode the effective address + * relative to the RIP of the following instruction. + */ + if (addr_offset == -EDOM) { + if (user_64bit_mode(regs)) + eff_addr = (long)regs->ip + insn->length; + else + eff_addr = 0; + } else if (addr_offset < 0) { goto out; - - eff_addr = regs_get_register(regs, addr_offset); + } else { + eff_addr = regs_get_register(regs, addr_offset); + } } eff_addr += insn->displacement.value; -- cgit v1.2.3 From 108904442850c2884679f81121df3ef42d88cb9c Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 13:25:45 -0700 Subject: x86/insn-eval: Incorporate segment base in linear address computation insn_get_addr_ref() returns the effective address as defined by the section 3.7.5.1 Vol 1 of the Intel 64 and IA-32 Architectures Software Developer's Manual. In order to compute the linear address, we must add to the effective address the segment base address as set in the segment descriptor. The segment descriptor to use depends on the register used as operand and segment override prefixes, if any. In most cases, the segment base address will be 0 if the USER_DS/USER32_DS segment is used or if segmentation is not used. However, the base address is not necessarily zero if a user programs defines its own segments. This is possible by using a local descriptor table. Since the effective address is a signed quantity, the unsigned segment base address is saved in a separate variable and added to the final, unsigned, effective address. Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-19-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/lib/insn-eval.c | 55 +++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 52 insertions(+), 3 deletions(-) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 6bf819f923e7..1c23ec03c568 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -728,6 +728,43 @@ int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs) return get_reg_offset(insn, regs, REG_TYPE_RM); } +/** + * get_seg_base_addr() - obtain base address of a segment + * @insn: Instruction. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @regoff: Operand offset, in pt_regs, used to resolve segment descriptor + * @base: Obtained segment base + * + * Obtain the base address of the segment associated with the operand @regoff + * and, if any or allowed, override prefixes in @insn. This function is + * different from insn_get_seg_base() as the latter does not resolve the segment + * associated with the instruction operand. + * + * Returns: + * + * 0 on success. @base will contain the base address of the resolved segment. + * + * -EINVAL on error. + */ +static int get_seg_base_addr(struct insn *insn, struct pt_regs *regs, + int regoff, unsigned long *base) +{ + int seg_reg_idx; + + if (!base) + return -EINVAL; + + seg_reg_idx = resolve_seg_reg(insn, regs, regoff); + if (seg_reg_idx < 0) + return seg_reg_idx; + + *base = insn_get_seg_base(regs, seg_reg_idx); + if (*base == -1L) + return -EINVAL; + + return 0; +} + /* * return the address being referenced be instruction * for rm=3 returning the content of the rm reg @@ -735,8 +772,8 @@ int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs) */ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) { - int addr_offset, base_offset, indx_offset; - unsigned long linear_addr = -1L; + int addr_offset, base_offset, indx_offset, ret; + unsigned long linear_addr = -1L, seg_base; long eff_addr, base, indx; insn_byte_t sib; @@ -750,6 +787,7 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) goto out; eff_addr = regs_get_register(regs, addr_offset); + } else { if (insn->sib.nbytes) { /* @@ -776,6 +814,13 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) indx = regs_get_register(regs, indx_offset); eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); + + /* + * The base determines the segment used to compute + * the linear address. + */ + addr_offset = base_offset; + } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); /* @@ -798,7 +843,11 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) eff_addr += insn->displacement.value; } - linear_addr = (unsigned long)eff_addr; + ret = get_seg_base_addr(insn, regs, addr_offset, &seg_base); + if (ret) + goto out; + + linear_addr = (unsigned long)eff_addr + seg_base; out: return (void __user *)linear_addr; -- cgit v1.2.3 From 71271269ef9a997fb4416b2f8ef3558dd846c7cb Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 27 Oct 2017 16:51:38 -0700 Subject: x86/insn-eval: Extend get_seg_base_addr() to also obtain segment limit In protected mode, it is common to want to obtain the limit of a segment along with its base address. This is useful, for instance, to verify that an effective address lies within a segment before computing a linear address. Up to this point, this library only computes linear addresses in long mode. Subsequent patches will include support for protected mode. Support to verify the segment limit will be needed. Signed-off-by: Ricardo Neri Cc: Adam Buchbinder Cc: Adrian Hunter Cc: Andrew Morton Cc: Andy Lutomirski Cc: Arnaldo Carvalho de Melo Cc: Borislav Petkov Cc: Brian Gerst Cc: Chen Yucong Cc: Chris Metcalf Cc: Colin Ian King Cc: Dave Hansen Cc: Dmitry Vyukov Cc: Huang Rui Cc: Jiri Slaby Cc: Jonathan Corbet Cc: Kees Cook Cc: Linus Torvalds Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Michael S. Tsirkin Cc: Paolo Bonzini Cc: Paul Gortmaker Cc: Peter Zijlstra Cc: Qiaowei Ren Cc: Ravi V. Shankar Cc: Shuah Khan Cc: Thomas Garnier Cc: Thomas Gleixner Cc: Vlastimil Babka Cc: ricardo.neri@intel.com Link: http://lkml.kernel.org/r/1509148310-30862-2-git-send-email-ricardo.neri-calderon@linux.intel.com Signed-off-by: Ingo Molnar --- arch/x86/lib/insn-eval.c | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 1c23ec03c568..91f08aafb65e 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -729,25 +729,29 @@ int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs) } /** - * get_seg_base_addr() - obtain base address of a segment + * get_seg_base_limit() - obtain base address and limit of a segment * @insn: Instruction. Must be valid. * @regs: Register values as seen when entering kernel mode * @regoff: Operand offset, in pt_regs, used to resolve segment descriptor * @base: Obtained segment base + * @limit: Obtained segment limit * - * Obtain the base address of the segment associated with the operand @regoff - * and, if any or allowed, override prefixes in @insn. This function is + * Obtain the base address and limit of the segment associated with the operand + * @regoff and, if any or allowed, override prefixes in @insn. This function is * different from insn_get_seg_base() as the latter does not resolve the segment - * associated with the instruction operand. + * associated with the instruction operand. If a limit is not needed (e.g., + * when running in long mode), @limit can be NULL. * * Returns: * - * 0 on success. @base will contain the base address of the resolved segment. + * 0 on success. @base and @limit will contain the base address and of the + * resolved segment, respectively. * * -EINVAL on error. */ -static int get_seg_base_addr(struct insn *insn, struct pt_regs *regs, - int regoff, unsigned long *base) +static int get_seg_base_limit(struct insn *insn, struct pt_regs *regs, + int regoff, unsigned long *base, + unsigned long *limit) { int seg_reg_idx; @@ -762,6 +766,13 @@ static int get_seg_base_addr(struct insn *insn, struct pt_regs *regs, if (*base == -1L) return -EINVAL; + if (!limit) + return 0; + + *limit = get_seg_limit(regs, seg_reg_idx); + if (!(*limit)) + return -EINVAL; + return 0; } @@ -843,7 +854,7 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) eff_addr += insn->displacement.value; } - ret = get_seg_base_addr(insn, regs, addr_offset, &seg_base); + ret = get_seg_base_limit(insn, regs, addr_offset, &seg_base, NULL); if (ret) goto out; -- cgit v1.2.3