1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Copyright (c) 2017 Google, Inc.
4 */
5
6 /*
7 * Regression test for commit 814fb7bb7db5 ("x86/fpu: Don't let userspace set
8 * bogus xcomp_bv"), or CVE-2017-15537. This bug allowed ptrace(pid,
9 * PTRACE_SETREGSET, NT_X86_XSTATE, &iov) to assign a task an invalid FPU state
10 * --- specifically, by setting reserved bits in xstate_header.xcomp_bv. This
11 * made restoring the FPU registers fail when switching to the task, causing the
12 * FPU registers to take on the values from other tasks.
13 *
14 * To detect the bug, we have a subprocess run a loop checking its xmm0 register
15 * for corruption. This detects the case where the FPU state became invalid and
16 * the kernel is not restoring the process's registers. Note that we have to
17 * set the expected value of xmm0 to all 0's since it is acceptable behavior for
18 * the kernel to simply reinitialize the FPU state upon seeing that it is
19 * invalid. To increase the chance of detecting the problem, we also create
20 * additional subprocesses that spin with different xmm0 contents.
21 *
22 * Thus bug affected the x86 architecture only. Other architectures could have
23 * similar bugs as well, but this test has to be x86-specific because it has to
24 * know about the architecture-dependent FPU state.
25 */
26
27 #include "tst_test.h"
28
29 #ifdef __x86_64__
30
31 #include <errno.h>
32 #include <inttypes.h>
33 #include <sched.h>
34 #include <stdbool.h>
35 #include <stdlib.h>
36 #include <sys/uio.h>
37 #include <sys/wait.h>
38 #include <sys/ptrace.h>
39
40 #include "tst_safe_macros.h"
41 #include "lapi/cpuid.h"
42
43 #ifndef PTRACE_GETREGSET
44 # define PTRACE_GETREGSET 0x4204
45 #endif
46
47 #ifndef PTRACE_SETREGSET
48 # define PTRACE_SETREGSET 0x4205
49 #endif
50
51 #ifndef NT_X86_XSTATE
52 # define NT_X86_XSTATE 0x202
53 #endif
54
55 #ifndef CPUID_LEAF_XSTATE
56 # define CPUID_LEAF_XSTATE 0xd
57 #endif
58
check_regs_loop(uint32_t initval)59 static void check_regs_loop(uint32_t initval)
60 {
61 const unsigned long num_iters = 1000000000;
62 uint32_t xmm0[4] = { initval, initval, initval, initval };
63 int status = 1;
64
65 asm volatile(" movdqu %0, %%xmm0\n"
66 " mov %0, %%rbx\n"
67 "1: dec %2\n"
68 " jz 2f\n"
69 " movdqu %%xmm0, %0\n"
70 " mov %0, %%rax\n"
71 " cmp %%rax, %%rbx\n"
72 " je 1b\n"
73 " jmp 3f\n"
74 "2: mov $0, %1\n"
75 "3:\n"
76 : "+m" (xmm0), "+r" (status)
77 : "r" (num_iters) : "rax", "rbx", "xmm0");
78
79 if (status) {
80 tst_res(TFAIL,
81 "xmm registers corrupted! initval=%08X, xmm0=%08X%08X%08X%08X\n",
82 initval, xmm0[0], xmm0[1], xmm0[2], xmm0[3]);
83 }
84 exit(status);
85 }
86
do_test(void)87 static void do_test(void)
88 {
89 int i;
90 int num_cpus = tst_ncpus();
91 pid_t pid;
92 uint32_t eax = 0, ebx = 0, ecx = 0, edx = 0;
93 uint64_t *xstate;
94 /*
95 * CPUID.(EAX=0DH, ECX=0H):EBX: maximum size (bytes, from the beginning
96 * of the XSAVE/XRSTOR save area) required by enabled features in XCR0.
97 */
98 __cpuid_count(CPUID_LEAF_XSTATE, ecx, eax, ebx, ecx, edx);
99 xstate = SAFE_MEMALIGN(64, ebx);
100 struct iovec iov = { .iov_base = xstate, .iov_len = ebx };
101 int status;
102 bool okay;
103
104 tst_res(TINFO, "CPUID.(EAX=%u, ECX=0):EAX=%u, EBX=%u, ECX=%u, EDX=%u",
105 CPUID_LEAF_XSTATE, eax, ebx, ecx, edx);
106 pid = SAFE_FORK();
107 if (pid == 0) {
108 TST_CHECKPOINT_WAKE(0);
109 check_regs_loop(0x00000000);
110 }
111 for (i = 0; i < num_cpus; i++) {
112 if (SAFE_FORK() == 0)
113 check_regs_loop(0xDEADBEEF);
114 }
115
116 TST_CHECKPOINT_WAIT(0);
117 sched_yield();
118
119 TEST(ptrace(PTRACE_ATTACH, pid, 0, 0));
120 if (TST_RET != 0) {
121 free(xstate);
122 tst_brk(TBROK | TTERRNO, "PTRACE_ATTACH failed");
123 }
124
125 SAFE_WAITPID(pid, NULL, 0);
126 TEST(ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov));
127 if (TST_RET != 0) {
128 free(xstate);
129 if (TST_ERR == EIO)
130 tst_brk(TCONF, "GETREGSET/SETREGSET is unsupported");
131
132 if (TST_ERR == EINVAL)
133 tst_brk(TCONF, "NT_X86_XSTATE is unsupported");
134
135 if (TST_ERR == ENODEV)
136 tst_brk(TCONF, "CPU doesn't support XSAVE instruction");
137
138 tst_brk(TBROK | TTERRNO,
139 "PTRACE_GETREGSET failed with unexpected error");
140 }
141
142 xstate[65] = -1; /* sets all bits in xstate_header.xcomp_bv */
143
144 /*
145 * Old kernels simply masked out all the reserved bits in the xstate
146 * header (causing the PTRACE_SETREGSET command here to succeed), while
147 * new kernels will reject them (causing the PTRACE_SETREGSET command
148 * here to fail with EINVAL). We accept either behavior, as neither
149 * behavior reliably tells us whether the real bug (which we test for
150 * below in either case) is present.
151 */
152 TEST(ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov));
153 if (TST_RET == 0) {
154 tst_res(TINFO, "PTRACE_SETREGSET with reserved bits succeeded");
155 } else if (TST_ERR == EINVAL) {
156 tst_res(TINFO,
157 "PTRACE_SETREGSET with reserved bits failed with EINVAL");
158 } else {
159 free(xstate);
160 tst_brk(TBROK | TTERRNO,
161 "PTRACE_SETREGSET failed with unexpected error");
162 }
163
164 /*
165 * It is possible for test child 'pid' to crash on AMD
166 * systems (e.g. AMD Opteron(TM) Processor 6234) with
167 * older kernels. This causes tracee to stop and sleep
168 * in ptrace_stop(). Without resuming the tracee, the
169 * test hangs at do_test()->tst_reap_children() called
170 * by the library. Use detach here, so we don't need to
171 * worry about potential stops after this point.
172 */
173 TEST(ptrace(PTRACE_DETACH, pid, 0, 0));
174 if (TST_RET != 0) {
175 free(xstate);
176 tst_brk(TBROK | TTERRNO, "PTRACE_DETACH failed");
177 }
178
179 /* If child 'pid' crashes, only report it as info. */
180 SAFE_WAITPID(pid, &status, 0);
181 if (WIFEXITED(status)) {
182 tst_res(TINFO, "test child %d exited, retcode: %d",
183 pid, WEXITSTATUS(status));
184 }
185 if (WIFSIGNALED(status)) {
186 tst_res(TINFO, "test child %d exited, termsig: %d",
187 pid, WTERMSIG(status));
188 }
189
190 okay = true;
191 for (i = 0; i < num_cpus; i++) {
192 SAFE_WAIT(&status);
193 okay &= (WIFEXITED(status) && WEXITSTATUS(status) == 0);
194 }
195 if (okay)
196 tst_res(TPASS, "wasn't able to set invalid FPU state");
197 free(xstate);
198 }
199
200 static struct tst_test test = {
201 .test_all = do_test,
202 .forks_child = 1,
203 .needs_checkpoints = 1,
204 .supported_archs = (const char *const []) {
205 "x86_64",
206 NULL
207 },
208 .tags = (const struct tst_tag[]) {
209 {"linux-git", "814fb7bb7db5"},
210 {"CVE", "2017-15537"},
211 {}
212 }
213
214 };
215
216 #else
217 TST_TEST_TCONF("Tests an x86_64 feature");
218 #endif /* if x86 */
219