From 78be3706b21a232310590fe00258b224177ac05f Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Tue, 26 Sep 2006 10:52:39 +0200 Subject: [PATCH] i386: Allow a kernel not to be in ring 0 We allow for the fact that the guest kernel may not run in ring 0. This requires some abstraction in a few places when setting %cs or checking privilege level (user vs kernel). This is Chris' [RFC PATCH 15/33] move segment checks to subarch, except rather than using #define USER_MODE_MASK which depends on a config option, we use Zach's more flexible approach of assuming ring 3 == userspace. I also used "get_kernel_rpl()" over "get_kernel_cs()" because I think it reads better in the code... 1) Remove the hardcoded 3 and introduce #define SEGMENT_RPL_MASK 3 2) Add a get_kernel_rpl() macro, and don't assume it's zero. And: Clean up of patch for letting kernel run other than ring 0: a. Add some comments about the SEGMENT_IS_*_CODE() macros. b. Add a USER_RPL macro. (Code was comparing a value to a mask in some places and to the magic number 3 in other places.) c. Add macros for table indicator field and use them. d. Change the entry.S tests for LDT stack segment to use the macros Signed-off-by: Rusty Russell Signed-off-by: Zachary Amsden Signed-off-by: Jeremy Fitzhardinge Signed-off-by: Andrew Morton Signed-off-by: Andi Kleen --- arch/i386/kernel/entry.S | 9 +++++---- arch/i386/kernel/process.c | 2 +- arch/i386/mm/extable.c | 2 +- arch/i386/mm/fault.c | 11 ++++------- 4 files changed, 11 insertions(+), 13 deletions(-) (limited to 'arch/i386') diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S index 3872fca5c74a..284f2e908ad0 100644 --- a/arch/i386/kernel/entry.S +++ b/arch/i386/kernel/entry.S @@ -240,8 +240,9 @@ ret_from_intr: check_userspace: movl EFLAGS(%esp), %eax # mix EFLAGS and CS movb CS(%esp), %al - testl $(VM_MASK | 3), %eax - jz resume_kernel + andl $(VM_MASK | SEGMENT_RPL_MASK), %eax + cmpl $USER_RPL, %eax + jb resume_kernel # not returning to v8086 or userspace ENTRY(resume_userspace) DISABLE_INTERRUPTS # make sure we don't miss an interrupt # setting need_resched or sigpending @@ -377,8 +378,8 @@ restore_all: # See comments in process.c:copy_thread() for details. movb OLDSS(%esp), %ah movb CS(%esp), %al - andl $(VM_MASK | (4 << 8) | 3), %eax - cmpl $((4 << 8) | 3), %eax + andl $(VM_MASK | (SEGMENT_TI_MASK << 8) | SEGMENT_RPL_MASK), %eax + cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax CFI_REMEMBER_STATE je ldt_ss # returning to user-space with LDT SS restore_nocheck: diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c index 220aeca59c3a..8c190ca7ae44 100644 --- a/arch/i386/kernel/process.c +++ b/arch/i386/kernel/process.c @@ -338,7 +338,7 @@ int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags) regs.xes = __USER_DS; regs.orig_eax = -1; regs.eip = (unsigned long) kernel_thread_helper; - regs.xcs = __KERNEL_CS; + regs.xcs = __KERNEL_CS | get_kernel_rpl(); regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2; /* Ok, create the new process.. */ diff --git a/arch/i386/mm/extable.c b/arch/i386/mm/extable.c index de03c5430abc..0ce4f22a2635 100644 --- a/arch/i386/mm/extable.c +++ b/arch/i386/mm/extable.c @@ -11,7 +11,7 @@ int fixup_exception(struct pt_regs *regs) const struct exception_table_entry *fixup; #ifdef CONFIG_PNPBIOS - if (unlikely((regs->xcs & ~15) == (GDT_ENTRY_PNPBIOS_BASE << 3))) + if (unlikely(SEGMENT_IS_PNP_CODE(regs->xcs))) { extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp; extern u32 pnp_bios_is_utter_crap; diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c index 0ce86168a0b1..5e17a3f43b41 100644 --- a/arch/i386/mm/fault.c +++ b/arch/i386/mm/fault.c @@ -27,6 +27,7 @@ #include #include #include +#include extern void die(const char *,struct pt_regs *,long); @@ -113,10 +114,10 @@ static inline unsigned long get_segment_eip(struct pt_regs *regs, } /* The standard kernel/user address space limit. */ - *eip_limit = (seg & 3) ? USER_DS.seg : KERNEL_DS.seg; + *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg; /* By far the most common cases. */ - if (likely(seg == __USER_CS || seg == __KERNEL_CS)) + if (likely(SEGMENT_IS_FLAT_CODE(seg))) return eip; /* Check the segment exists, is within the current LDT/GDT size, @@ -430,11 +431,7 @@ good_area: write = 0; switch (error_code & 3) { default: /* 3: write, present */ -#ifdef TEST_VERIFY_AREA - if (regs->cs == KERNEL_CS) - printk("WP fault at %08lx\n", regs->eip); -#endif - /* fall through */ + /* fall through */ case 2: /* write, not present */ if (!(vma->vm_flags & VM_WRITE)) goto bad_area; -- cgit v1.2.3