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
22static 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
32static 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
45static 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
56static void sigsegv(int sig, siginfo_t *info, void *uc_void)
57{
58	printf("\tGot SIGSEGV\n");
59}
60
61int 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}
103