selftests/x86/single_step_syscall: Check SYSENTER directly

We used to test SYSENTER only through the vDSO.  Test it directly
too, just in case.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/tools/testing/selftests/x86/single_step_syscall.c b/tools/testing/selftests/x86/single_step_syscall.c
index 50ce6c3dd9040a7ee9c083d7717a2551d6d7a8b0..1063328e275c90b33b07a2ac9d8c71d72d06d6bc 100644 (file)
--- a/tools/testing/selftests/x86/single_step_syscall.c
+++ b/tools/testing/selftests/x86/single_step_syscall.c
@@ -43,7 +43,19 @@ static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
                err(1, "sigaction");
 }
 
-static volatile sig_atomic_t sig_traps;
+static void clearhandler(int sig)
+{
+       struct sigaction sa;
+       memset(&sa, 0, sizeof(sa));
+       sa.sa_handler = SIG_DFL;
+       sigemptyset(&sa.sa_mask);
+       if (sigaction(sig, &sa, 0))
+               err(1, "sigaction");
+}
+
+static volatile sig_atomic_t sig_traps, sig_eflags;
+sigjmp_buf jmpbuf;
+static unsigned char altstack_data[SIGSTKSZ];
 
 #ifdef __x86_64__
 # define REG_IP REG_RIP
@@ -90,6 +102,25 @@ static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
        }
 }
 
+static char const * const signames[] = {
+       [SIGSEGV] = "SIGSEGV",
+       [SIGBUS] = "SIBGUS",
+       [SIGTRAP] = "SIGTRAP",
+       [SIGILL] = "SIGILL",
+};
+
+static void print_and_longjmp(int sig, siginfo_t *si, void *ctx_void)
+{
+       ucontext_t *ctx = ctx_void;
+
+       printf("\tGot %s with RIP=%lx, TF=%ld\n", signames[sig],
+              (unsigned long)ctx->uc_mcontext.gregs[REG_IP],
+              (unsigned long)ctx->uc_mcontext.gregs[REG_EFL] & X86_EFLAGS_TF);
+
+       sig_eflags = (unsigned long)ctx->uc_mcontext.gregs[REG_EFL];
+       siglongjmp(jmpbuf, 1);
+}
+
 static void check_result(void)
 {
        unsigned long new_eflags = get_eflags();
@@ -109,6 +140,22 @@ static void check_result(void)
        sig_traps = 0;
 }
 
+static void fast_syscall_no_tf(void)
+{
+       sig_traps = 0;
+       printf("[RUN]\tFast syscall with TF cleared\n");
+       fflush(stdout);  /* Force a syscall */
+       if (get_eflags() & X86_EFLAGS_TF) {
+               printf("[FAIL]\tTF is now set\n");
+               exit(1);
+       }
+       if (sig_traps) {
+               printf("[FAIL]\tGot SIGTRAP\n");
+               exit(1);
+       }
+       printf("[OK]\tNothing unexpected happened\n");
+}
+
 int main()
 {
 #ifdef CAN_BUILD_32
@@ -163,17 +210,46 @@ int main()
        check_result();
 
        /* Now make sure that another fast syscall doesn't set TF again. */
-       printf("[RUN]\tFast syscall with TF cleared\n");
-       fflush(stdout);  /* Force a syscall */
-       if (get_eflags() & X86_EFLAGS_TF) {
-               printf("[FAIL]\tTF is now set\n");
-               exit(1);
+       fast_syscall_no_tf();
+
+       /*
+        * And do a forced SYSENTER to make sure that this works even if
+        * fast syscalls don't use SYSENTER.
+        *
+        * Invoking SYSENTER directly breaks all the rules.  Just handle
+        * the SIGSEGV.
+        */
+       if (sigsetjmp(jmpbuf, 1) == 0) {
+               unsigned long nr = SYS_getpid;
+               printf("[RUN]\tSet TF and check SYSENTER\n");
+               stack_t stack = {
+                       .ss_sp = altstack_data,
+                       .ss_size = SIGSTKSZ,
+               };
+               if (sigaltstack(&stack, NULL) != 0)
+                       err(1, "sigaltstack");
+               sethandler(SIGSEGV, print_and_longjmp,
+                          SA_RESETHAND | SA_ONSTACK);
+               sethandler(SIGILL, print_and_longjmp, SA_RESETHAND);
+               set_eflags(get_eflags() | X86_EFLAGS_TF);
+               /* Clear EBP first to make sure we segfault cleanly. */
+               asm volatile ("xorl %%ebp, %%ebp; SYSENTER" : "+a" (nr) :: "flags", "rcx"
+#ifdef __x86_64__
+                               , "r11"
+#endif
+                       );
+
+               /* We're unreachable here.  SYSENTER forgets RIP. */
        }
-       if (sig_traps) {
-               printf("[FAIL]\tGot SIGTRAP\n");
+       clearhandler(SIGSEGV);
+       clearhandler(SIGILL);
+       if (!(sig_eflags & X86_EFLAGS_TF)) {
+               printf("[FAIL]\tTF was cleared\n");
                exit(1);
        }
-       printf("[OK]\tNothing unexpected happened\n");
+
+       /* Now make sure that another fast syscall doesn't set TF again. */
+       fast_syscall_no_tf();
 
        return 0;
 }