tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
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linux
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * sigreturn.c - tests that x86 avoids Intel SYSRET pitfalls
4 * Copyright (c) 2014-2016 Andrew Lutomirski
5 */
6
7#define _GNU_SOURCE
8
9#include <stdlib.h>
10#include <unistd.h>
11#include <stdio.h>
12#include <string.h>
13#include <inttypes.h>
14#include <sys/signal.h>
15#include <sys/ucontext.h>
16#include <sys/syscall.h>
17#include <err.h>
18#include <stddef.h>
19#include <stdbool.h>
20#include <setjmp.h>
21#include <sys/user.h>
22#include <sys/mman.h>
23#include <assert.h>
24
25/*
26 * These items are in clang_helpers_64.S, in order to avoid clang inline asm
27 * limitations:
28 */
29void test_syscall_ins(void);
30extern const char test_page[];
31
32static void const *current_test_page_addr = test_page;
33
34static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
35 int flags)
36{
37 struct sigaction sa;
38 memset(&sa, 0, sizeof(sa));
39 sa.sa_sigaction = handler;
40 sa.sa_flags = SA_SIGINFO | flags;
41 sigemptyset(&sa.sa_mask);
42 if (sigaction(sig, &sa, 0))
43 err(1, "sigaction");
44}
45
46static void clearhandler(int sig)
47{
48 struct sigaction sa;
49 memset(&sa, 0, sizeof(sa));
50 sa.sa_handler = SIG_DFL;
51 sigemptyset(&sa.sa_mask);
52 if (sigaction(sig, &sa, 0))
53 err(1, "sigaction");
54}
55
56/* State used by our signal handlers. */
57static gregset_t initial_regs;
58
59static volatile unsigned long rip;
60
61static void sigsegv_for_sigreturn_test(int sig, siginfo_t *info, void *ctx_void)
62{
63 ucontext_t *ctx = (ucontext_t*)ctx_void;
64
65 if (rip != ctx->uc_mcontext.gregs[REG_RIP]) {
66 printf("[FAIL]\tRequested RIP=0x%lx but got RIP=0x%lx\n",
67 rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]);
68 fflush(stdout);
69 _exit(1);
70 }
71
72 memcpy(&ctx->uc_mcontext.gregs, &initial_regs, sizeof(gregset_t));
73
74 printf("[OK]\tGot SIGSEGV at RIP=0x%lx\n", rip);
75}
76
77static void sigusr1(int sig, siginfo_t *info, void *ctx_void)
78{
79 ucontext_t *ctx = (ucontext_t*)ctx_void;
80
81 memcpy(&initial_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
82
83 /* Set IP and CX to match so that SYSRET can happen. */
84 ctx->uc_mcontext.gregs[REG_RIP] = rip;
85 ctx->uc_mcontext.gregs[REG_RCX] = rip;
86
87 /* R11 and EFLAGS should already match. */
88 assert(ctx->uc_mcontext.gregs[REG_EFL] ==
89 ctx->uc_mcontext.gregs[REG_R11]);
90
91 sethandler(SIGSEGV, sigsegv_for_sigreturn_test, SA_RESETHAND);
92
93 return;
94}
95
96static void test_sigreturn_to(unsigned long ip)
97{
98 rip = ip;
99 printf("[RUN]\tsigreturn to 0x%lx\n", ip);
100 raise(SIGUSR1);
101}
102
103static jmp_buf jmpbuf;
104
105static void sigsegv_for_fallthrough(int sig, siginfo_t *info, void *ctx_void)
106{
107 ucontext_t *ctx = (ucontext_t*)ctx_void;
108
109 if (rip != ctx->uc_mcontext.gregs[REG_RIP]) {
110 printf("[FAIL]\tExpected SIGSEGV at 0x%lx but got RIP=0x%lx\n",
111 rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]);
112 fflush(stdout);
113 _exit(1);
114 }
115
116 siglongjmp(jmpbuf, 1);
117}
118
119static void test_syscall_fallthrough_to(unsigned long ip)
120{
121 void *new_address = (void *)(ip - 4096);
122 void *ret;
123
124 printf("[RUN]\tTrying a SYSCALL that falls through to 0x%lx\n", ip);
125
126 ret = mremap((void *)current_test_page_addr, 4096, 4096,
127 MREMAP_MAYMOVE | MREMAP_FIXED, new_address);
128 if (ret == MAP_FAILED) {
129 if (ip <= (1UL << 47) - PAGE_SIZE) {
130 err(1, "mremap to %p", new_address);
131 } else {
132 printf("[OK]\tmremap to %p failed\n", new_address);
133 return;
134 }
135 }
136
137 if (ret != new_address)
138 errx(1, "mremap malfunctioned: asked for %p but got %p\n",
139 new_address, ret);
140
141 current_test_page_addr = new_address;
142 rip = ip;
143
144 if (sigsetjmp(jmpbuf, 1) == 0) {
145 asm volatile ("call *%[syscall_insn]" :: "a" (SYS_getpid),
146 [syscall_insn] "rm" (ip - 2));
147 errx(1, "[FAIL]\tSyscall trampoline returned");
148 }
149
150 printf("[OK]\tWe survived\n");
151}
152
153int main()
154{
155 /*
156 * When the kernel returns from a slow-path syscall, it will
157 * detect whether SYSRET is appropriate. If it incorrectly
158 * thinks that SYSRET is appropriate when RIP is noncanonical,
159 * it'll crash on Intel CPUs.
160 */
161 sethandler(SIGUSR1, sigusr1, 0);
162 for (int i = 47; i < 64; i++)
163 test_sigreturn_to(1UL<<i);
164
165 clearhandler(SIGUSR1);
166
167 sethandler(SIGSEGV, sigsegv_for_fallthrough, 0);
168
169 /* One extra test to check that we didn't screw up the mremap logic. */
170 test_syscall_fallthrough_to((1UL << 47) - 2*PAGE_SIZE);
171
172 /* These are the interesting cases. */
173 for (int i = 47; i < 64; i++) {
174 test_syscall_fallthrough_to((1UL<<i) - PAGE_SIZE);
175 test_syscall_fallthrough_to(1UL<<i);
176 }
177
178 return 0;
179}