segv_errors.c

 1// SPDX-License-Identifier: GPL-2.0
 2
 3/*
 4 * Copyright 2017 John Sperbeck
 5 *
 6 * Test that an access to a mapped but inaccessible area causes a SEGV and
 7 * reports si_code == SEGV_ACCERR.
 8 */
 9
10#include <stdbool.h>
11#include <stdio.h>
12#include <stdlib.h>
13#include <string.h>
14#include <unistd.h>
15#include <signal.h>
16#include <sys/mman.h>
17#include <assert.h>
18#include <ucontext.h>
19
20#include "utils.h"
21
22static bool faulted;
23static int si_code;
24
25static void segv_handler(int n, siginfo_t *info, void *ctxt_v)
26{
27	ucontext_t *ctxt = (ucontext_t *)ctxt_v;
28	struct pt_regs *regs = ctxt->uc_mcontext.regs;
29
30	faulted = true;
31	si_code = info->si_code;
32	regs->nip += 4;
33}
34
35int test_segv_errors(void)
36{
37	struct sigaction act = {
38		.sa_sigaction = segv_handler,
39		.sa_flags = SA_SIGINFO,
40	};
41	char c, *p = NULL;
42
43	p = mmap(NULL, getpagesize(), 0, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
44	FAIL_IF(p == MAP_FAILED);
45
46	FAIL_IF(sigaction(SIGSEGV, &act, NULL) != 0);
47
48	faulted = false;
49	si_code = 0;
50
51	/*
52	 * We just need a compiler barrier, but mb() works and has the nice
53	 * property of being easy to spot in the disassembly.
54	 */
55	mb();
56	c = *p;
57	mb();
58
59	FAIL_IF(!faulted);
60	FAIL_IF(si_code != SEGV_ACCERR);
61
62	faulted = false;
63	si_code = 0;
64
65	mb();
66	*p = c;
67	mb();
68
69	FAIL_IF(!faulted);
70	FAIL_IF(si_code != SEGV_ACCERR);
71
72	return 0;
73}
74
75int main(void)
76{
77	return test_harness(test_segv_errors, "segv_errors");
78}