summaryrefslogtreecommitdiff
path: root/tools/testing/selftests/x86/syscall_arg_fault.c
blob: bc0ecc2e862ef781c610d3f337e65af4f0948683 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
// SPDX-License-Identifier: GPL-2.0-only
/*
 * syscall_arg_fault.c - tests faults 32-bit fast syscall stack args
 * Copyright (c) 2015 Andrew Lutomirski
 */

#define _GNU_SOURCE

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/signal.h>
#include <sys/ucontext.h>
#include <err.h>
#include <setjmp.h>
#include <errno.h>

#ifdef __x86_64__
# define WIDTH "q"
#else
# define WIDTH "l"
#endif

/* Our sigaltstack scratch space. */
static unsigned char altstack_data[SIGSTKSZ];

static unsigned long get_eflags(void)
{
	unsigned long eflags;
	asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
	return eflags;
}

static void set_eflags(unsigned long eflags)
{
	asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
		      : : "rm" (eflags) : "flags");
}

#define X86_EFLAGS_TF (1UL << 8)

static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
		       int flags)
{
	struct sigaction sa;
	memset(&sa, 0, sizeof(sa));
	sa.sa_sigaction = handler;
	sa.sa_flags = SA_SIGINFO | flags;
	sigemptyset(&sa.sa_mask);
	if (sigaction(sig, &sa, 0))
		err(1, "sigaction");
}

static volatile sig_atomic_t sig_traps;
static sigjmp_buf jmpbuf;

static volatile sig_atomic_t n_errs;

#ifdef __x86_64__
#define REG_AX REG_RAX
#define REG_IP REG_RIP
#else
#define REG_AX REG_EAX
#define REG_IP REG_EIP
#endif

static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
{
	ucontext_t *ctx = (ucontext_t*)ctx_void;
	long ax = (long)ctx->uc_mcontext.gregs[REG_AX];

	if (ax != -EFAULT && ax != -ENOSYS) {
		printf("[FAIL]\tAX had the wrong value: 0x%lx\n",
		       (unsigned long)ax);
		n_errs++;
	} else {
		printf("[OK]\tSeems okay\n");
	}

	siglongjmp(jmpbuf, 1);
}

static volatile sig_atomic_t sigtrap_consecutive_syscalls;

static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
{
	/*
	 * KVM has some bugs that can cause us to stop making progress.
	 * detect them and complain, but don't infinite loop or fail the
	 * test.
	 */

	ucontext_t *ctx = (ucontext_t*)ctx_void;
	unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];

	if (*ip == 0x340f || *ip == 0x050f) {
		/* The trap was on SYSCALL or SYSENTER */
		sigtrap_consecutive_syscalls++;
		if (sigtrap_consecutive_syscalls > 3) {
			printf("[WARN]\tGot stuck single-stepping -- you probably have a KVM bug\n");
			siglongjmp(jmpbuf, 1);
		}
	} else {
		sigtrap_consecutive_syscalls = 0;
	}
}

static void sigill(int sig, siginfo_t *info, void *ctx_void)
{
	ucontext_t *ctx = (ucontext_t*)ctx_void;
	unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];

	if (*ip == 0x0b0f) {
		/* one of the ud2 instructions faulted */
		printf("[OK]\tSYSCALL returned normally\n");
	} else {
		printf("[SKIP]\tIllegal instruction\n");
	}
	siglongjmp(jmpbuf, 1);
}

int main()
{
	stack_t stack = {
		.ss_sp = altstack_data,
		.ss_size = SIGSTKSZ,
	};
	if (sigaltstack(&stack, NULL) != 0)
		err(1, "sigaltstack");

	sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
	/*
	 * The actual exception can vary.  On Atom CPUs, we get #SS
	 * instead of #PF when the vDSO fails to access the stack when
	 * ESP is too close to 2^32, and #SS causes SIGBUS.
	 */
	sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
	sethandler(SIGILL, sigill, SA_ONSTACK);

	/*
	 * Exercise another nasty special case.  The 32-bit SYSCALL
	 * and SYSENTER instructions (even in compat mode) each
	 * clobber one register.  A Linux system call has a syscall
	 * number and six arguments, and the user stack pointer
	 * needs to live in some register on return.  That means
	 * that we need eight registers, but SYSCALL and SYSENTER
	 * only preserve seven registers.  As a result, one argument
	 * ends up on the stack.  The stack is user memory, which
	 * means that the kernel can fail to read it.
	 *
	 * The 32-bit fast system calls don't have a defined ABI:
	 * we're supposed to invoke them through the vDSO.  So we'll
	 * fudge it: we set all regs to invalid pointer values and
	 * invoke the entry instruction.  The return will fail no
	 * matter what, and we completely lose our program state,
	 * but we can fix it up with a signal handler.
	 */

	printf("[RUN]\tSYSENTER with invalid state\n");
	if (sigsetjmp(jmpbuf, 1) == 0) {
		asm volatile (
			"movl $-1, %%eax\n\t"
			"movl $-1, %%ebx\n\t"
			"movl $-1, %%ecx\n\t"
			"movl $-1, %%edx\n\t"
			"movl $-1, %%esi\n\t"
			"movl $-1, %%edi\n\t"
			"movl $-1, %%ebp\n\t"
			"movl $-1, %%esp\n\t"
			"sysenter"
			: : : "memory", "flags");
	}

	printf("[RUN]\tSYSCALL with invalid state\n");
	if (sigsetjmp(jmpbuf, 1) == 0) {
		asm volatile (
			"movl $-1, %%eax\n\t"
			"movl $-1, %%ebx\n\t"
			"movl $-1, %%ecx\n\t"
			"movl $-1, %%edx\n\t"
			"movl $-1, %%esi\n\t"
			"movl $-1, %%edi\n\t"
			"movl $-1, %%ebp\n\t"
			"movl $-1, %%esp\n\t"
			"syscall\n\t"
			"ud2"		/* make sure we recover cleanly */
			: : : "memory", "flags");
	}

	printf("[RUN]\tSYSENTER with TF and invalid state\n");
	sethandler(SIGTRAP, sigtrap, SA_ONSTACK);

	if (sigsetjmp(jmpbuf, 1) == 0) {
		sigtrap_consecutive_syscalls = 0;
		set_eflags(get_eflags() | X86_EFLAGS_TF);
		asm volatile (
			"movl $-1, %%eax\n\t"
			"movl $-1, %%ebx\n\t"
			"movl $-1, %%ecx\n\t"
			"movl $-1, %%edx\n\t"
			"movl $-1, %%esi\n\t"
			"movl $-1, %%edi\n\t"
			"movl $-1, %%ebp\n\t"
			"movl $-1, %%esp\n\t"
			"sysenter"
			: : : "memory", "flags");
	}
	set_eflags(get_eflags() & ~X86_EFLAGS_TF);

	printf("[RUN]\tSYSCALL with TF and invalid state\n");
	if (sigsetjmp(jmpbuf, 1) == 0) {
		sigtrap_consecutive_syscalls = 0;
		set_eflags(get_eflags() | X86_EFLAGS_TF);
		asm volatile (
			"movl $-1, %%eax\n\t"
			"movl $-1, %%ebx\n\t"
			"movl $-1, %%ecx\n\t"
			"movl $-1, %%edx\n\t"
			"movl $-1, %%esi\n\t"
			"movl $-1, %%edi\n\t"
			"movl $-1, %%ebp\n\t"
			"movl $-1, %%esp\n\t"
			"syscall\n\t"
			"ud2"		/* make sure we recover cleanly */
			: : : "memory", "flags");
	}
	set_eflags(get_eflags() & ~X86_EFLAGS_TF);

	return 0;
}