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1/*
2 * syscall_arg_fault.c - tests faults 32-bit fast syscall stack args
3 * Copyright (c) 2015 Andrew Lutomirski
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms and conditions of the GNU General Public License,
7 * version 2, as published by the Free Software Foundation.
8 *
9 * This program is distributed in the hope it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 */
14
15#define _GNU_SOURCE
16
17#include <stdlib.h>
18#include <stdio.h>
19#include <string.h>
20#include <sys/signal.h>
21#include <sys/ucontext.h>
22#include <err.h>
23#include <setjmp.h>
24#include <errno.h>
25
26/* Our sigaltstack scratch space. */
27static unsigned char altstack_data[SIGSTKSZ];
28
29static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
30 int flags)
31{
32 struct sigaction sa;
33 memset(&sa, 0, sizeof(sa));
34 sa.sa_sigaction = handler;
35 sa.sa_flags = SA_SIGINFO | flags;
36 sigemptyset(&sa.sa_mask);
37 if (sigaction(sig, &sa, 0))
38 err(1, "sigaction");
39}
40
41static volatile sig_atomic_t sig_traps;
42static sigjmp_buf jmpbuf;
43
44static volatile sig_atomic_t n_errs;
45
46static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
47{
48 ucontext_t *ctx = (ucontext_t*)ctx_void;
49
50 if (ctx->uc_mcontext.gregs[REG_EAX] != -EFAULT) {
51 printf("[FAIL]\tAX had the wrong value: 0x%x\n",
52 ctx->uc_mcontext.gregs[REG_EAX]);
53 n_errs++;
54 } else {
55 printf("[OK]\tSeems okay\n");
56 }
57
58 siglongjmp(jmpbuf, 1);
59}
60
61static void sigill(int sig, siginfo_t *info, void *ctx_void)
62{
63 printf("[SKIP]\tIllegal instruction\n");
64 siglongjmp(jmpbuf, 1);
65}
66
67int main()
68{
69 stack_t stack = {
70 .ss_sp = altstack_data,
71 .ss_size = SIGSTKSZ,
72 };
73 if (sigaltstack(&stack, NULL) != 0)
74 err(1, "sigaltstack");
75
76 sethandler(SIGSEGV, sigsegv, SA_ONSTACK);
77 sethandler(SIGILL, sigill, SA_ONSTACK);
78
79 /*
80 * Exercise another nasty special case. The 32-bit SYSCALL
81 * and SYSENTER instructions (even in compat mode) each
82 * clobber one register. A Linux system call has a syscall
83 * number and six arguments, and the user stack pointer
84 * needs to live in some register on return. That means
85 * that we need eight registers, but SYSCALL and SYSENTER
86 * only preserve seven registers. As a result, one argument
87 * ends up on the stack. The stack is user memory, which
88 * means that the kernel can fail to read it.
89 *
90 * The 32-bit fast system calls don't have a defined ABI:
91 * we're supposed to invoke them through the vDSO. So we'll
92 * fudge it: we set all regs to invalid pointer values and
93 * invoke the entry instruction. The return will fail no
94 * matter what, and we completely lose our program state,
95 * but we can fix it up with a signal handler.
96 */
97
98 printf("[RUN]\tSYSENTER with invalid state\n");
99 if (sigsetjmp(jmpbuf, 1) == 0) {
100 asm volatile (
101 "movl $-1, %%eax\n\t"
102 "movl $-1, %%ebx\n\t"
103 "movl $-1, %%ecx\n\t"
104 "movl $-1, %%edx\n\t"
105 "movl $-1, %%esi\n\t"
106 "movl $-1, %%edi\n\t"
107 "movl $-1, %%ebp\n\t"
108 "movl $-1, %%esp\n\t"
109 "sysenter"
110 : : : "memory", "flags");
111 }
112
113 printf("[RUN]\tSYSCALL with invalid state\n");
114 if (sigsetjmp(jmpbuf, 1) == 0) {
115 asm volatile (
116 "movl $-1, %%eax\n\t"
117 "movl $-1, %%ebx\n\t"
118 "movl $-1, %%ecx\n\t"
119 "movl $-1, %%edx\n\t"
120 "movl $-1, %%esi\n\t"
121 "movl $-1, %%edi\n\t"
122 "movl $-1, %%ebp\n\t"
123 "movl $-1, %%esp\n\t"
124 "syscall\n\t"
125 "pushl $0" /* make sure we segfault cleanly */
126 : : : "memory", "flags");
127 }
128
129 return 0;
130}
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * syscall_arg_fault.c - tests faults 32-bit fast syscall stack args
4 * Copyright (c) 2015 Andrew Lutomirski
5 */
6
7#define _GNU_SOURCE
8
9#include <stdlib.h>
10#include <stdio.h>
11#include <string.h>
12#include <sys/signal.h>
13#include <sys/ucontext.h>
14#include <err.h>
15#include <setjmp.h>
16#include <errno.h>
17
18#include "helpers.h"
19
20static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
21 int flags)
22{
23 struct sigaction sa;
24 memset(&sa, 0, sizeof(sa));
25 sa.sa_sigaction = handler;
26 sa.sa_flags = SA_SIGINFO | flags;
27 sigemptyset(&sa.sa_mask);
28 if (sigaction(sig, &sa, 0))
29 err(1, "sigaction");
30}
31
32static volatile sig_atomic_t sig_traps;
33static sigjmp_buf jmpbuf;
34
35static volatile sig_atomic_t n_errs;
36
37#ifdef __x86_64__
38#define REG_AX REG_RAX
39#define REG_IP REG_RIP
40#else
41#define REG_AX REG_EAX
42#define REG_IP REG_EIP
43#endif
44
45static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
46{
47 ucontext_t *ctx = (ucontext_t*)ctx_void;
48 long ax = (long)ctx->uc_mcontext.gregs[REG_AX];
49
50 if (ax != -EFAULT && ax != -ENOSYS) {
51 printf("[FAIL]\tAX had the wrong value: 0x%lx\n",
52 (unsigned long)ax);
53 printf("\tIP = 0x%lx\n", (unsigned long)ctx->uc_mcontext.gregs[REG_IP]);
54 n_errs++;
55 } else {
56 printf("[OK]\tSeems okay\n");
57 }
58
59 siglongjmp(jmpbuf, 1);
60}
61
62static volatile sig_atomic_t sigtrap_consecutive_syscalls;
63
64static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
65{
66 /*
67 * KVM has some bugs that can cause us to stop making progress.
68 * detect them and complain, but don't infinite loop or fail the
69 * test.
70 */
71
72 ucontext_t *ctx = (ucontext_t*)ctx_void;
73 unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];
74
75 if (*ip == 0x340f || *ip == 0x050f) {
76 /* The trap was on SYSCALL or SYSENTER */
77 sigtrap_consecutive_syscalls++;
78 if (sigtrap_consecutive_syscalls > 3) {
79 printf("[WARN]\tGot stuck single-stepping -- you probably have a KVM bug\n");
80 siglongjmp(jmpbuf, 1);
81 }
82 } else {
83 sigtrap_consecutive_syscalls = 0;
84 }
85}
86
87static void sigill(int sig, siginfo_t *info, void *ctx_void)
88{
89 ucontext_t *ctx = (ucontext_t*)ctx_void;
90 unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];
91
92 if (*ip == 0x0b0f) {
93 /* one of the ud2 instructions faulted */
94 printf("[OK]\tSYSCALL returned normally\n");
95 } else {
96 printf("[SKIP]\tIllegal instruction\n");
97 }
98 siglongjmp(jmpbuf, 1);
99}
100
101int main()
102{
103 stack_t stack = {
104 /* Our sigaltstack scratch space. */
105 .ss_sp = malloc(sizeof(char) * SIGSTKSZ),
106 .ss_size = SIGSTKSZ,
107 };
108 if (sigaltstack(&stack, NULL) != 0)
109 err(1, "sigaltstack");
110
111 sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
112 /*
113 * The actual exception can vary. On Atom CPUs, we get #SS
114 * instead of #PF when the vDSO fails to access the stack when
115 * ESP is too close to 2^32, and #SS causes SIGBUS.
116 */
117 sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
118 sethandler(SIGILL, sigill, SA_ONSTACK);
119
120 /*
121 * Exercise another nasty special case. The 32-bit SYSCALL
122 * and SYSENTER instructions (even in compat mode) each
123 * clobber one register. A Linux system call has a syscall
124 * number and six arguments, and the user stack pointer
125 * needs to live in some register on return. That means
126 * that we need eight registers, but SYSCALL and SYSENTER
127 * only preserve seven registers. As a result, one argument
128 * ends up on the stack. The stack is user memory, which
129 * means that the kernel can fail to read it.
130 *
131 * The 32-bit fast system calls don't have a defined ABI:
132 * we're supposed to invoke them through the vDSO. So we'll
133 * fudge it: we set all regs to invalid pointer values and
134 * invoke the entry instruction. The return will fail no
135 * matter what, and we completely lose our program state,
136 * but we can fix it up with a signal handler.
137 */
138
139 printf("[RUN]\tSYSENTER with invalid state\n");
140 if (sigsetjmp(jmpbuf, 1) == 0) {
141 asm volatile (
142 "movl $-1, %%eax\n\t"
143 "movl $-1, %%ebx\n\t"
144 "movl $-1, %%ecx\n\t"
145 "movl $-1, %%edx\n\t"
146 "movl $-1, %%esi\n\t"
147 "movl $-1, %%edi\n\t"
148 "movl $-1, %%ebp\n\t"
149 "movl $-1, %%esp\n\t"
150 "sysenter"
151 : : : "memory", "flags");
152 }
153
154 printf("[RUN]\tSYSCALL with invalid state\n");
155 if (sigsetjmp(jmpbuf, 1) == 0) {
156 asm volatile (
157 "movl $-1, %%eax\n\t"
158 "movl $-1, %%ebx\n\t"
159 "movl $-1, %%ecx\n\t"
160 "movl $-1, %%edx\n\t"
161 "movl $-1, %%esi\n\t"
162 "movl $-1, %%edi\n\t"
163 "movl $-1, %%ebp\n\t"
164 "movl $-1, %%esp\n\t"
165 "syscall\n\t"
166 "ud2" /* make sure we recover cleanly */
167 : : : "memory", "flags");
168 }
169
170 printf("[RUN]\tSYSENTER with TF and invalid state\n");
171 sethandler(SIGTRAP, sigtrap, SA_ONSTACK);
172
173 if (sigsetjmp(jmpbuf, 1) == 0) {
174 sigtrap_consecutive_syscalls = 0;
175 set_eflags(get_eflags() | X86_EFLAGS_TF);
176 asm volatile (
177 "movl $-1, %%eax\n\t"
178 "movl $-1, %%ebx\n\t"
179 "movl $-1, %%ecx\n\t"
180 "movl $-1, %%edx\n\t"
181 "movl $-1, %%esi\n\t"
182 "movl $-1, %%edi\n\t"
183 "movl $-1, %%ebp\n\t"
184 "movl $-1, %%esp\n\t"
185 "sysenter"
186 : : : "memory", "flags");
187 }
188 set_eflags(get_eflags() & ~X86_EFLAGS_TF);
189
190 printf("[RUN]\tSYSCALL with TF and invalid state\n");
191 if (sigsetjmp(jmpbuf, 1) == 0) {
192 sigtrap_consecutive_syscalls = 0;
193 set_eflags(get_eflags() | X86_EFLAGS_TF);
194 asm volatile (
195 "movl $-1, %%eax\n\t"
196 "movl $-1, %%ebx\n\t"
197 "movl $-1, %%ecx\n\t"
198 "movl $-1, %%edx\n\t"
199 "movl $-1, %%esi\n\t"
200 "movl $-1, %%edi\n\t"
201 "movl $-1, %%ebp\n\t"
202 "movl $-1, %%esp\n\t"
203 "syscall\n\t"
204 "ud2" /* make sure we recover cleanly */
205 : : : "memory", "flags");
206 }
207 set_eflags(get_eflags() & ~X86_EFLAGS_TF);
208
209#ifdef __x86_64__
210 printf("[RUN]\tSYSENTER with TF, invalid state, and GSBASE < 0\n");
211
212 if (sigsetjmp(jmpbuf, 1) == 0) {
213 sigtrap_consecutive_syscalls = 0;
214
215 asm volatile ("wrgsbase %%rax\n\t"
216 :: "a" (0xffffffffffff0000UL));
217
218 set_eflags(get_eflags() | X86_EFLAGS_TF);
219 asm volatile (
220 "movl $-1, %%eax\n\t"
221 "movl $-1, %%ebx\n\t"
222 "movl $-1, %%ecx\n\t"
223 "movl $-1, %%edx\n\t"
224 "movl $-1, %%esi\n\t"
225 "movl $-1, %%edi\n\t"
226 "movl $-1, %%ebp\n\t"
227 "movl $-1, %%esp\n\t"
228 "sysenter"
229 : : : "memory", "flags");
230 }
231 set_eflags(get_eflags() & ~X86_EFLAGS_TF);
232#endif
233
234 free(stack.ss_sp);
235 return 0;
236}