diff options
| -rw-r--r-- | arch/x86/entry/entry_64.S | 5 | ||||
| -rw-r--r-- | arch/x86/include/asm/fsgsbase.h | 4 | ||||
| -rw-r--r-- | arch/x86/kernel/process_64.c | 8 | ||||
| -rw-r--r-- | tools/testing/selftests/x86/fsgsbase.c | 68 |
4 files changed, 77 insertions, 8 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index d977079a7d02..748c2db3c54e 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -842,8 +842,9 @@ SYM_CODE_START_LOCAL(paranoid_entry) * retrieve and set the current CPUs kernel GSBASE. The stored value * has to be restored in paranoid_exit unconditionally. * - * The MSR write ensures that no subsequent load is based on a - * mispredicted GSBASE. No extra FENCE required. + * The unconditional write to GS base below ensures that no subsequent + * loads based on a mispredicted GS base can happen, therefore no LFENCE + * is needed here. */ SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx ret diff --git a/arch/x86/include/asm/fsgsbase.h b/arch/x86/include/asm/fsgsbase.h index d552646411a9..35cff5f2becf 100644 --- a/arch/x86/include/asm/fsgsbase.h +++ b/arch/x86/include/asm/fsgsbase.h @@ -57,7 +57,7 @@ static inline unsigned long x86_fsbase_read_cpu(void) { unsigned long fsbase; - if (static_cpu_has(X86_FEATURE_FSGSBASE)) + if (boot_cpu_has(X86_FEATURE_FSGSBASE)) fsbase = rdfsbase(); else rdmsrl(MSR_FS_BASE, fsbase); @@ -67,7 +67,7 @@ static inline unsigned long x86_fsbase_read_cpu(void) static inline void x86_fsbase_write_cpu(unsigned long fsbase) { - if (static_cpu_has(X86_FEATURE_FSGSBASE)) + if (boot_cpu_has(X86_FEATURE_FSGSBASE)) wrfsbase(fsbase); else wrmsrl(MSR_FS_BASE, fsbase); diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 9afefe325acb..df342bedea88 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -407,7 +407,7 @@ unsigned long x86_gsbase_read_cpu_inactive(void) { unsigned long gsbase; - if (static_cpu_has(X86_FEATURE_FSGSBASE)) { + if (boot_cpu_has(X86_FEATURE_FSGSBASE)) { unsigned long flags; local_irq_save(flags); @@ -422,7 +422,7 @@ unsigned long x86_gsbase_read_cpu_inactive(void) void x86_gsbase_write_cpu_inactive(unsigned long gsbase) { - if (static_cpu_has(X86_FEATURE_FSGSBASE)) { + if (boot_cpu_has(X86_FEATURE_FSGSBASE)) { unsigned long flags; local_irq_save(flags); @@ -439,7 +439,7 @@ unsigned long x86_fsbase_read_task(struct task_struct *task) if (task == current) fsbase = x86_fsbase_read_cpu(); - else if (static_cpu_has(X86_FEATURE_FSGSBASE) || + else if (boot_cpu_has(X86_FEATURE_FSGSBASE) || (task->thread.fsindex == 0)) fsbase = task->thread.fsbase; else @@ -454,7 +454,7 @@ unsigned long x86_gsbase_read_task(struct task_struct *task) if (task == current) gsbase = x86_gsbase_read_cpu_inactive(); - else if (static_cpu_has(X86_FEATURE_FSGSBASE) || + else if (boot_cpu_has(X86_FEATURE_FSGSBASE) || (task->thread.gsindex == 0)) gsbase = task->thread.gsbase; else diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c index 998319553523..7161cfc2e60b 100644 --- a/tools/testing/selftests/x86/fsgsbase.c +++ b/tools/testing/selftests/x86/fsgsbase.c @@ -443,6 +443,68 @@ static void test_unexpected_base(void) #define USER_REGS_OFFSET(r) offsetof(struct user_regs_struct, r) +static void test_ptrace_write_gs_read_base(void) +{ + int status; + pid_t child = fork(); + + if (child < 0) + err(1, "fork"); + + if (child == 0) { + printf("[RUN]\tPTRACE_POKE GS, read GSBASE back\n"); + + printf("[RUN]\tARCH_SET_GS to 1\n"); + if (syscall(SYS_arch_prctl, ARCH_SET_GS, 1) != 0) + err(1, "ARCH_SET_GS"); + + if (ptrace(PTRACE_TRACEME, 0, NULL, NULL) != 0) + err(1, "PTRACE_TRACEME"); + + raise(SIGTRAP); + _exit(0); + } + + wait(&status); + + if (WSTOPSIG(status) == SIGTRAP) { + unsigned long base; + unsigned long gs_offset = USER_REGS_OFFSET(gs); + unsigned long base_offset = USER_REGS_OFFSET(gs_base); + + /* Read the initial base. It should be 1. */ + base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL); + if (base == 1) { + printf("[OK]\tGSBASE started at 1\n"); + } else { + nerrs++; + printf("[FAIL]\tGSBASE started at 0x%lx\n", base); + } + + printf("[RUN]\tSet GS = 0x7, read GSBASE\n"); + + /* Poke an LDT selector into GS. */ + if (ptrace(PTRACE_POKEUSER, child, gs_offset, 0x7) != 0) + err(1, "PTRACE_POKEUSER"); + + /* And read the base. */ + base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL); + + if (base == 0 || base == 1) { + printf("[OK]\tGSBASE reads as 0x%lx with invalid GS\n", base); + } else { + nerrs++; + printf("[FAIL]\tGSBASE=0x%lx (should be 0 or 1)\n", base); + } + } + + ptrace(PTRACE_CONT, child, NULL, NULL); + + wait(&status); + if (!WIFEXITED(status)) + printf("[WARN]\tChild didn't exit cleanly.\n"); +} + static void test_ptrace_write_gsbase(void) { int status; @@ -517,6 +579,9 @@ static void test_ptrace_write_gsbase(void) END: ptrace(PTRACE_CONT, child, NULL, NULL); + wait(&status); + if (!WIFEXITED(status)) + printf("[WARN]\tChild didn't exit cleanly.\n"); } int main() @@ -526,6 +591,9 @@ int main() shared_scratch = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0); + /* Do these tests before we have an LDT. */ + test_ptrace_write_gs_read_base(); + /* Probe FSGSBASE */ sethandler(SIGILL, sigill, 0); if (sigsetjmp(jmpbuf, 1) == 0) { |