tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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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#include "helpers.h"
26
27/*
28 * These items are in clang_helpers_64.S, in order to avoid clang inline asm
29 * limitations:
30 */
31void test_syscall_ins(void);
32extern const char test_page[];
33
34static void const *current_test_page_addr = test_page;
35
36/* State used by our signal handlers. */
37static gregset_t initial_regs;
38
39static volatile unsigned long rip;
40
41static void sigsegv_for_sigreturn_test(int sig, siginfo_t *info, void *ctx_void)
42{
43 ucontext_t *ctx = (ucontext_t*)ctx_void;
44
45 if (rip != ctx->uc_mcontext.gregs[REG_RIP]) {
46 printf("[FAIL]\tRequested RIP=0x%lx but got RIP=0x%lx\n",
47 rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]);
48 fflush(stdout);
49 _exit(1);
50 }
51
52 memcpy(&ctx->uc_mcontext.gregs, &initial_regs, sizeof(gregset_t));
53
54 printf("[OK]\tGot SIGSEGV at RIP=0x%lx\n", rip);
55}
56
57static void sigusr1(int sig, siginfo_t *info, void *ctx_void)
58{
59 ucontext_t *ctx = (ucontext_t*)ctx_void;
60
61 memcpy(&initial_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
62
63 /* Set IP and CX to match so that SYSRET can happen. */
64 ctx->uc_mcontext.gregs[REG_RIP] = rip;
65 ctx->uc_mcontext.gregs[REG_RCX] = rip;
66
67 /* R11 and EFLAGS should already match. */
68 assert(ctx->uc_mcontext.gregs[REG_EFL] ==
69 ctx->uc_mcontext.gregs[REG_R11]);
70
71 sethandler(SIGSEGV, sigsegv_for_sigreturn_test, SA_RESETHAND);
72
73 return;
74}
75
76static void test_sigreturn_to(unsigned long ip)
77{
78 rip = ip;
79 printf("[RUN]\tsigreturn to 0x%lx\n", ip);
80 raise(SIGUSR1);
81}
82
83static jmp_buf jmpbuf;
84
85static void sigsegv_for_fallthrough(int sig, siginfo_t *info, void *ctx_void)
86{
87 ucontext_t *ctx = (ucontext_t*)ctx_void;
88
89 if (rip != ctx->uc_mcontext.gregs[REG_RIP]) {
90 printf("[FAIL]\tExpected SIGSEGV at 0x%lx but got RIP=0x%lx\n",
91 rip, (unsigned long)ctx->uc_mcontext.gregs[REG_RIP]);
92 fflush(stdout);
93 _exit(1);
94 }
95
96 siglongjmp(jmpbuf, 1);
97}
98
99static void test_syscall_fallthrough_to(unsigned long ip)
100{
101 void *new_address = (void *)(ip - 4096);
102 void *ret;
103
104 printf("[RUN]\tTrying a SYSCALL that falls through to 0x%lx\n", ip);
105
106 ret = mremap((void *)current_test_page_addr, 4096, 4096,
107 MREMAP_MAYMOVE | MREMAP_FIXED, new_address);
108 if (ret == MAP_FAILED) {
109 if (ip <= (1UL << 47) - PAGE_SIZE) {
110 err(1, "mremap to %p", new_address);
111 } else {
112 printf("[OK]\tmremap to %p failed\n", new_address);
113 return;
114 }
115 }
116
117 if (ret != new_address)
118 errx(1, "mremap malfunctioned: asked for %p but got %p\n",
119 new_address, ret);
120
121 current_test_page_addr = new_address;
122 rip = ip;
123
124 if (sigsetjmp(jmpbuf, 1) == 0) {
125 asm volatile ("call *%[syscall_insn]" :: "a" (SYS_getpid),
126 [syscall_insn] "rm" (ip - 2));
127 errx(1, "[FAIL]\tSyscall trampoline returned");
128 }
129
130 printf("[OK]\tWe survived\n");
131}
132
133int main()
134{
135 /*
136 * When the kernel returns from a slow-path syscall, it will
137 * detect whether SYSRET is appropriate. If it incorrectly
138 * thinks that SYSRET is appropriate when RIP is noncanonical,
139 * it'll crash on Intel CPUs.
140 */
141 sethandler(SIGUSR1, sigusr1, 0);
142 for (int i = 47; i < 64; i++)
143 test_sigreturn_to(1UL<<i);
144
145 clearhandler(SIGUSR1);
146
147 sethandler(SIGSEGV, sigsegv_for_fallthrough, 0);
148
149 /* One extra test to check that we didn't screw up the mremap logic. */
150 test_syscall_fallthrough_to((1UL << 47) - 2*PAGE_SIZE);
151
152 /* These are the interesting cases. */
153 for (int i = 47; i < 64; i++) {
154 test_syscall_fallthrough_to((1UL<<i) - PAGE_SIZE);
155 test_syscall_fallthrough_to(1UL<<i);
156 }
157
158 return 0;
159}