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
20 /* Our sigaltstack scratch space. */
21 static unsigned char altstack_data[SIGSTKSZ];
22
sethandler(int sig,void (* handler)(int,siginfo_t *,void *),int flags)23 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
24 int flags)
25 {
26 struct sigaction sa;
27 memset(&sa, 0, sizeof(sa));
28 sa.sa_sigaction = handler;
29 sa.sa_flags = SA_SIGINFO | flags;
30 sigemptyset(&sa.sa_mask);
31 if (sigaction(sig, &sa, 0))
32 err(1, "sigaction");
33 }
34
35 static volatile sig_atomic_t sig_traps;
36 static sigjmp_buf jmpbuf;
37
38 static volatile sig_atomic_t n_errs;
39
40 #ifdef __x86_64__
41 #define REG_AX REG_RAX
42 #define REG_IP REG_RIP
43 #else
44 #define REG_AX REG_EAX
45 #define REG_IP REG_EIP
46 #endif
47
sigsegv_or_sigbus(int sig,siginfo_t * info,void * ctx_void)48 static void sigsegv_or_sigbus(int sig, siginfo_t *info, void *ctx_void)
49 {
50 ucontext_t *ctx = (ucontext_t*)ctx_void;
51 long ax = (long)ctx->uc_mcontext.gregs[REG_AX];
52
53 if (ax != -EFAULT && ax != -ENOSYS) {
54 printf("[FAIL]\tAX had the wrong value: 0x%lx\n",
55 (unsigned long)ax);
56 printf("\tIP = 0x%lx\n", (unsigned long)ctx->uc_mcontext.gregs[REG_IP]);
57 n_errs++;
58 } else {
59 printf("[OK]\tSeems okay\n");
60 }
61
62 siglongjmp(jmpbuf, 1);
63 }
64
65 static volatile sig_atomic_t sigtrap_consecutive_syscalls;
66
sigtrap(int sig,siginfo_t * info,void * ctx_void)67 static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
68 {
69 /*
70 * KVM has some bugs that can cause us to stop making progress.
71 * detect them and complain, but don't infinite loop or fail the
72 * test.
73 */
74
75 ucontext_t *ctx = (ucontext_t*)ctx_void;
76 unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];
77
78 if (*ip == 0x340f || *ip == 0x050f) {
79 /* The trap was on SYSCALL or SYSENTER */
80 sigtrap_consecutive_syscalls++;
81 if (sigtrap_consecutive_syscalls > 3) {
82 printf("[WARN]\tGot stuck single-stepping -- you probably have a KVM bug\n");
83 siglongjmp(jmpbuf, 1);
84 }
85 } else {
86 sigtrap_consecutive_syscalls = 0;
87 }
88 }
89
sigill(int sig,siginfo_t * info,void * ctx_void)90 static void sigill(int sig, siginfo_t *info, void *ctx_void)
91 {
92 ucontext_t *ctx = (ucontext_t*)ctx_void;
93 unsigned short *ip = (unsigned short *)ctx->uc_mcontext.gregs[REG_IP];
94
95 if (*ip == 0x0b0f) {
96 /* one of the ud2 instructions faulted */
97 printf("[OK]\tSYSCALL returned normally\n");
98 } else {
99 printf("[SKIP]\tIllegal instruction\n");
100 }
101 siglongjmp(jmpbuf, 1);
102 }
103
main()104 int main()
105 {
106 stack_t stack = {
107 .ss_sp = altstack_data,
108 .ss_size = SIGSTKSZ,
109 };
110 if (sigaltstack(&stack, NULL) != 0)
111 err(1, "sigaltstack");
112
113 sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
114 /*
115 * The actual exception can vary. On Atom CPUs, we get #SS
116 * instead of #PF when the vDSO fails to access the stack when
117 * ESP is too close to 2^32, and #SS causes SIGBUS.
118 */
119 sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
120 sethandler(SIGILL, sigill, SA_ONSTACK);
121
122 /*
123 * Exercise another nasty special case. The 32-bit SYSCALL
124 * and SYSENTER instructions (even in compat mode) each
125 * clobber one register. A Linux system call has a syscall
126 * number and six arguments, and the user stack pointer
127 * needs to live in some register on return. That means
128 * that we need eight registers, but SYSCALL and SYSENTER
129 * only preserve seven registers. As a result, one argument
130 * ends up on the stack. The stack is user memory, which
131 * means that the kernel can fail to read it.
132 *
133 * The 32-bit fast system calls don't have a defined ABI:
134 * we're supposed to invoke them through the vDSO. So we'll
135 * fudge it: we set all regs to invalid pointer values and
136 * invoke the entry instruction. The return will fail no
137 * matter what, and we completely lose our program state,
138 * but we can fix it up with a signal handler.
139 */
140
141 printf("[RUN]\tSYSENTER with invalid state\n");
142 if (sigsetjmp(jmpbuf, 1) == 0) {
143 asm volatile (
144 "movl $-1, %%eax\n\t"
145 "movl $-1, %%ebx\n\t"
146 "movl $-1, %%ecx\n\t"
147 "movl $-1, %%edx\n\t"
148 "movl $-1, %%esi\n\t"
149 "movl $-1, %%edi\n\t"
150 "movl $-1, %%ebp\n\t"
151 "movl $-1, %%esp\n\t"
152 "sysenter"
153 : : : "memory", "flags");
154 }
155
156 printf("[RUN]\tSYSCALL with invalid state\n");
157 if (sigsetjmp(jmpbuf, 1) == 0) {
158 asm volatile (
159 "movl $-1, %%eax\n\t"
160 "movl $-1, %%ebx\n\t"
161 "movl $-1, %%ecx\n\t"
162 "movl $-1, %%edx\n\t"
163 "movl $-1, %%esi\n\t"
164 "movl $-1, %%edi\n\t"
165 "movl $-1, %%ebp\n\t"
166 "movl $-1, %%esp\n\t"
167 "syscall\n\t"
168 "ud2" /* make sure we recover cleanly */
169 : : : "memory", "flags");
170 }
171
172 printf("[RUN]\tSYSENTER with TF and invalid state\n");
173 sethandler(SIGTRAP, sigtrap, SA_ONSTACK);
174
175 if (sigsetjmp(jmpbuf, 1) == 0) {
176 sigtrap_consecutive_syscalls = 0;
177 set_eflags(get_eflags() | X86_EFLAGS_TF);
178 asm volatile (
179 "movl $-1, %%eax\n\t"
180 "movl $-1, %%ebx\n\t"
181 "movl $-1, %%ecx\n\t"
182 "movl $-1, %%edx\n\t"
183 "movl $-1, %%esi\n\t"
184 "movl $-1, %%edi\n\t"
185 "movl $-1, %%ebp\n\t"
186 "movl $-1, %%esp\n\t"
187 "sysenter"
188 : : : "memory", "flags");
189 }
190 set_eflags(get_eflags() & ~X86_EFLAGS_TF);
191
192 printf("[RUN]\tSYSCALL with TF and invalid state\n");
193 if (sigsetjmp(jmpbuf, 1) == 0) {
194 sigtrap_consecutive_syscalls = 0;
195 set_eflags(get_eflags() | X86_EFLAGS_TF);
196 asm volatile (
197 "movl $-1, %%eax\n\t"
198 "movl $-1, %%ebx\n\t"
199 "movl $-1, %%ecx\n\t"
200 "movl $-1, %%edx\n\t"
201 "movl $-1, %%esi\n\t"
202 "movl $-1, %%edi\n\t"
203 "movl $-1, %%ebp\n\t"
204 "movl $-1, %%esp\n\t"
205 "syscall\n\t"
206 "ud2" /* make sure we recover cleanly */
207 : : : "memory", "flags");
208 }
209 set_eflags(get_eflags() & ~X86_EFLAGS_TF);
210
211 #ifdef __x86_64__
212 printf("[RUN]\tSYSENTER with TF, invalid state, and GSBASE < 0\n");
213
214 if (sigsetjmp(jmpbuf, 1) == 0) {
215 sigtrap_consecutive_syscalls = 0;
216
217 asm volatile ("wrgsbase %%rax\n\t"
218 :: "a" (0xffffffffffff0000UL));
219
220 set_eflags(get_eflags() | X86_EFLAGS_TF);
221 asm volatile (
222 "movl $-1, %%eax\n\t"
223 "movl $-1, %%ebx\n\t"
224 "movl $-1, %%ecx\n\t"
225 "movl $-1, %%edx\n\t"
226 "movl $-1, %%esi\n\t"
227 "movl $-1, %%edi\n\t"
228 "movl $-1, %%ebp\n\t"
229 "movl $-1, %%esp\n\t"
230 "sysenter"
231 : : : "memory", "flags");
232 }
233 set_eflags(get_eflags() & ~X86_EFLAGS_TF);
234 #endif
235
236 return 0;
237 }
238