From a5d25e01c8146ad8846da4760422e12242fceafe Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 27 May 2020 16:02:36 -0700 Subject: selftests/x86: Add a syscall_arg_fault_64 test for negative GSBASE If the kernel erroneously allows WRGSBASE and user code writes a negative value, paranoid_entry will get confused. Check for this by writing a negative value to GSBASE and doing SYSENTER with TF set. A successful run looks like: [RUN] SYSENTER with TF, invalid state, and GSBASE < 0 [SKIP] Illegal instruction A failed run causes a kernel hang, and I believe it's because we double-fault and then get a never ending series of page faults and, when we exhaust the double fault stack we double fault again, starting the process over. Signed-off-by: Andy Lutomirski Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/f4f71efc91b9eae5e3dae21c9aee1c70cf5f370e.1590620529.git.luto@kernel.org --- tools/testing/selftests/x86/syscall_arg_fault.c | 26 +++++++++++++++++++++++++ 1 file changed, 26 insertions(+) (limited to 'tools/testing/selftests/x86/syscall_arg_fault.c') diff --git a/tools/testing/selftests/x86/syscall_arg_fault.c b/tools/testing/selftests/x86/syscall_arg_fault.c index bc0ecc2e862e..62fba40866d5 100644 --- a/tools/testing/selftests/x86/syscall_arg_fault.c +++ b/tools/testing/selftests/x86/syscall_arg_fault.c @@ -72,6 +72,7 @@ static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void) if (ax != -EFAULT && ax != -ENOSYS) { printf("[FAIL]\tAX had the wrong value: 0x%lx\n", (unsigned long)ax); + printf("\tIP = 0x%lx\n", (unsigned long)ctx->uc_mcontext.gregs[REG_IP]); n_errs++; } else { printf("[OK]\tSeems okay\n"); @@ -226,5 +227,30 @@ int main() } set_eflags(get_eflags() & ~X86_EFLAGS_TF); +#ifdef __x86_64__ + printf("[RUN]\tSYSENTER with TF, invalid state, and GSBASE < 0\n"); + + if (sigsetjmp(jmpbuf, 1) == 0) { + sigtrap_consecutive_syscalls = 0; + + asm volatile ("wrgsbase %%rax\n\t" + :: "a" (0xffffffffffff0000UL)); + + set_eflags(get_eflags() | X86_EFLAGS_TF); + asm volatile ( + "movl $-1, %%eax\n\t" + "movl $-1, %%ebx\n\t" + "movl $-1, %%ecx\n\t" + "movl $-1, %%edx\n\t" + "movl $-1, %%esi\n\t" + "movl $-1, %%edi\n\t" + "movl $-1, %%ebp\n\t" + "movl $-1, %%esp\n\t" + "sysenter" + : : : "memory", "flags"); + } + set_eflags(get_eflags() & ~X86_EFLAGS_TF); +#endif + return 0; } -- cgit v1.2.3-59-g8ed1b