tools/testing/selftests/x86/corrupt_xstate_header.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Corrupt the XSTATE header in a signal frame
   4  *
   5  * Based on analysis and a test case from Thomas Gleixner.
   6  */
   7
   8 #define _GNU_SOURCE
   9
  10 #include <stdlib.h>
  11 #include <stdio.h>
  12 #include <string.h>
  13 #include <sched.h>
  14 #include <signal.h>
  15 #include <err.h>
  16 #include <unistd.h>
  17 #include <stdint.h>
  18 #include <sys/wait.h>
  19
  20 #include "../kselftest.h" /* For __cpuid_count() */
  21
  22 static inline int xsave_enabled(void)
  23 {
  24         unsigned int eax, ebx, ecx, edx;
  25
  26         __cpuid_count(0x1, 0x0, eax, ebx, ecx, edx);
  27
  28         /* Is CR4.OSXSAVE enabled ? */
  29         return ecx & (1U << 27);
  30 }
  31
  32 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
  33                        int flags)
  34 {
  35         struct sigaction sa;
  36
  37         memset(&sa, 0, sizeof(sa));
  38         sa.sa_sigaction = handler;
  39         sa.sa_flags = SA_SIGINFO | flags;
  40         sigemptyset(&sa.sa_mask);
  41         if (sigaction(sig, &sa, 0))
  42                 err(1, "sigaction");
  43 }
  44
  45 static void sigusr1(int sig, siginfo_t *info, void *uc_void)
  46 {
  47         ucontext_t *uc = uc_void;
  48         uint8_t *fpstate = (uint8_t *)uc->uc_mcontext.fpregs;
  49         uint64_t *xfeatures = (uint64_t *)(fpstate + 512);
  50
  51         printf("\tWreck XSTATE header\n");
  52         /* Wreck the first reserved bytes in the header */
  53         *(xfeatures + 2) = 0xfffffff;
  54 }
  55
  56 static void sigsegv(int sig, siginfo_t *info, void *uc_void)
  57 {
  58         printf("\tGot SIGSEGV\n");
  59 }
  60
  61 int main(void)
  62 {
  63         cpu_set_t set;
  64
  65         sethandler(SIGUSR1, sigusr1, 0);
  66         sethandler(SIGSEGV, sigsegv, 0);
  67
  68         if (!xsave_enabled()) {
  69                 printf("[SKIP] CR4.OSXSAVE disabled.\n");
  70                 return 0;
  71         }
  72
  73         CPU_ZERO(&set);
  74         CPU_SET(0, &set);
  75
  76         /*
  77          * Enforce that the child runs on the same CPU
  78          * which in turn forces a schedule.
  79          */
  80         sched_setaffinity(getpid(), sizeof(set), &set);
  81
  82         printf("[RUN]\tSend ourselves a signal\n");
  83         raise(SIGUSR1);
  84
  85         printf("[OK]\tBack from the signal.  Now schedule.\n");
  86         pid_t child = fork();
  87         if (child < 0)
  88                 err(1, "fork");
  89         if (child == 0)
  90                 return 0;
  91         if (child)
  92                 waitpid(child, NULL, 0);
  93         printf("[OK]\tBack in the main thread.\n");
  94
  95         /*
  96          * We could try to confirm that extended state is still preserved
  97          * when we schedule.  For now, the only indication of failure is
  98          * a warning in the kernel logs.
  99          */
 100
 101         return 0;
 102 }