tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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#include "helpers.h"
22
23static inline int xsave_enabled(void)
24{
25 unsigned int eax, ebx, ecx, edx;
26
27 __cpuid_count(0x1, 0x0, eax, ebx, ecx, edx);
28
29 /* Is CR4.OSXSAVE enabled ? */
30 return ecx & (1U << 27);
31}
32
33static void sigusr1(int sig, siginfo_t *info, void *uc_void)
34{
35 ucontext_t *uc = uc_void;
36 uint8_t *fpstate = (uint8_t *)uc->uc_mcontext.fpregs;
37 uint64_t *xfeatures = (uint64_t *)(fpstate + 512);
38
39 printf("\tWreck XSTATE header\n");
40 /* Wreck the first reserved bytes in the header */
41 *(xfeatures + 2) = 0xfffffff;
42}
43
44static void sigsegv(int sig, siginfo_t *info, void *uc_void)
45{
46 printf("\tGot SIGSEGV\n");
47}
48
49int main(void)
50{
51 cpu_set_t set;
52
53 sethandler(SIGUSR1, sigusr1, 0);
54 sethandler(SIGSEGV, sigsegv, 0);
55
56 if (!xsave_enabled()) {
57 printf("[SKIP] CR4.OSXSAVE disabled.\n");
58 return 0;
59 }
60
61 CPU_ZERO(&set);
62 CPU_SET(0, &set);
63
64 /*
65 * Enforce that the child runs on the same CPU
66 * which in turn forces a schedule.
67 */
68 sched_setaffinity(getpid(), sizeof(set), &set);
69
70 printf("[RUN]\tSend ourselves a signal\n");
71 raise(SIGUSR1);
72
73 printf("[OK]\tBack from the signal. Now schedule.\n");
74 pid_t child = fork();
75 if (child < 0)
76 err(1, "fork");
77 if (child == 0)
78 return 0;
79 if (child)
80 waitpid(child, NULL, 0);
81 printf("[OK]\tBack in the main thread.\n");
82
83 /*
84 * We could try to confirm that extended state is still preserved
85 * when we schedule. For now, the only indication of failure is
86 * a warning in the kernel logs.
87 */
88
89 return 0;
90}