1 // SPDX-License-Identifier: GPL-2.0
2 #include <unistd.h>
3 #include <pthread.h>
4 #include <sys/mman.h>
5 #include <stdatomic.h>
6 #include <test_progs.h>
7 #include <sys/syscall.h>
8 #include <linux/module.h>
9 #include <linux/userfaultfd.h>
10
11 #include "ksym_race.skel.h"
12 #include "bpf_mod_race.skel.h"
13 #include "kfunc_call_race.skel.h"
14 #include "testing_helpers.h"
15
16 /* This test crafts a race between btf_try_get_module and do_init_module, and
17 * checks whether btf_try_get_module handles the invocation for a well-formed
18 * but uninitialized module correctly. Unless the module has completed its
19 * initcalls, the verifier should fail the program load and return ENXIO.
20 *
21 * userfaultfd is used to trigger a fault in an fmod_ret program, and make it
22 * sleep, then the BPF program is loaded and the return value from verifier is
23 * inspected. After this, the userfaultfd is closed so that the module loading
24 * thread makes forward progress, and fmod_ret injects an error so that the
25 * module load fails and it is freed.
26 *
27 * If the verifier succeeded in loading the supplied program, it will end up
28 * taking reference to freed module, and trigger a crash when the program fd
29 * is closed later. This is true for both kfuncs and ksyms. In both cases,
30 * the crash is triggered inside bpf_prog_free_deferred, when module reference
31 * is finally released.
32 */
33
34 struct test_config {
35 const char *str_open;
36 void *(*bpf_open_and_load)();
37 void (*bpf_destroy)(void *);
38 };
39
40 enum bpf_test_state {
41 _TS_INVALID,
42 TS_MODULE_LOAD,
43 TS_MODULE_LOAD_FAIL,
44 };
45
46 static _Atomic enum bpf_test_state state = _TS_INVALID;
47
48 static void *load_module_thread(void *p)
49 {
50
51 if (!ASSERT_NEQ(load_bpf_testmod(false), 0, "load_module_thread must fail"))
52 atomic_store(&state, TS_MODULE_LOAD);
53 else
54 atomic_store(&state, TS_MODULE_LOAD_FAIL);
55 return p;
56 }
57
58 static int sys_userfaultfd(int flags)
59 {
60 return syscall(__NR_userfaultfd, flags);
61 }
62
63 static int test_setup_uffd(void *fault_addr)
64 {
65 struct uffdio_register uffd_register = {};
66 struct uffdio_api uffd_api = {};
67 int uffd;
68
69 uffd = sys_userfaultfd(O_CLOEXEC);
70 if (uffd < 0)
71 return -errno;
72
73 uffd_api.api = UFFD_API;
74 uffd_api.features = 0;
75 if (ioctl(uffd, UFFDIO_API, &uffd_api)) {
76 close(uffd);
77 return -1;
78 }
79
80 uffd_register.range.start = (unsigned long)fault_addr;
81 uffd_register.range.len = 4096;
82 uffd_register.mode = UFFDIO_REGISTER_MODE_MISSING;
83 if (ioctl(uffd, UFFDIO_REGISTER, &uffd_register)) {
84 close(uffd);
85 return -1;
86 }
87 return uffd;
88 }
89
90 static void test_bpf_mod_race_config(const struct test_config *config)
91 {
92 void *fault_addr, *skel_fail;
93 struct bpf_mod_race *skel;
94 struct uffd_msg uffd_msg;
95 pthread_t load_mod_thrd;
96 _Atomic int *blockingp;
97 int uffd, ret;
98
99 fault_addr = mmap(0, 4096, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
100 if (!ASSERT_NEQ(fault_addr, MAP_FAILED, "mmap for uffd registration"))
101 return;
102
103 if (!ASSERT_OK(unload_bpf_testmod(false), "unload bpf_testmod"))
104 goto end_mmap;
105
106 skel = bpf_mod_race__open();
107 if (!ASSERT_OK_PTR(skel, "bpf_mod_kfunc_race__open"))
108 goto end_module;
109
110 skel->rodata->bpf_mod_race_config.tgid = getpid();
111 skel->rodata->bpf_mod_race_config.inject_error = -4242;
112 skel->rodata->bpf_mod_race_config.fault_addr = fault_addr;
113 if (!ASSERT_OK(bpf_mod_race__load(skel), "bpf_mod___load"))
114 goto end_destroy;
115 blockingp = (_Atomic int *)&skel->bss->bpf_blocking;
116
117 if (!ASSERT_OK(bpf_mod_race__attach(skel), "bpf_mod_kfunc_race__attach"))
118 goto end_destroy;
119
120 uffd = test_setup_uffd(fault_addr);
121 if (!ASSERT_GE(uffd, 0, "userfaultfd open + register address"))
122 goto end_destroy;
123
124 if (!ASSERT_OK(pthread_create(&load_mod_thrd, NULL, load_module_thread, NULL),
125 "load module thread"))
126 goto end_uffd;
127
128 /* Now, we either fail loading module, or block in bpf prog, spin to find out */
129 while (!atomic_load(&state) && !atomic_load(blockingp))
130 ;
131 if (!ASSERT_EQ(state, _TS_INVALID, "module load should block"))
132 goto end_join;
133 if (!ASSERT_EQ(*blockingp, 1, "module load blocked")) {
134 pthread_kill(load_mod_thrd, SIGKILL);
135 goto end_uffd;
136 }
137
138 /* We might have set bpf_blocking to 1, but may have not blocked in
139 * bpf_copy_from_user. Read userfaultfd descriptor to verify that.
140 */
141 if (!ASSERT_EQ(read(uffd, &uffd_msg, sizeof(uffd_msg)), sizeof(uffd_msg),
142 "read uffd block event"))
143 goto end_join;
144 if (!ASSERT_EQ(uffd_msg.event, UFFD_EVENT_PAGEFAULT, "read uffd event is pagefault"))
145 goto end_join;
146
147 /* We know that load_mod_thrd is blocked in the fmod_ret program, the
148 * module state is still MODULE_STATE_COMING because mod->init hasn't
149 * returned. This is the time we try to load a program calling kfunc and
150 * check if we get ENXIO from verifier.
151 */
152 skel_fail = config->bpf_open_and_load();
153 ret = errno;
154 if (!ASSERT_EQ(skel_fail, NULL, config->str_open)) {
155 /* Close uffd to unblock load_mod_thrd */
156 close(uffd);
157 uffd = -1;
158 while (atomic_load(blockingp) != 2)
159 ;
160 ASSERT_OK(kern_sync_rcu(), "kern_sync_rcu");
161 config->bpf_destroy(skel_fail);
162 goto end_join;
163
164 }
165 ASSERT_EQ(ret, ENXIO, "verifier returns ENXIO");
166 ASSERT_EQ(skel->data->res_try_get_module, false, "btf_try_get_module == false");
167
168 close(uffd);
169 uffd = -1;
170 end_join:
171 pthread_join(load_mod_thrd, NULL);
172 if (uffd < 0)
173 ASSERT_EQ(atomic_load(&state), TS_MODULE_LOAD_FAIL, "load_mod_thrd success");
174 end_uffd:
175 if (uffd >= 0)
176 close(uffd);
177 end_destroy:
178 bpf_mod_race__destroy(skel);
179 ASSERT_OK(kern_sync_rcu(), "kern_sync_rcu");
180 end_module:
181 unload_bpf_testmod(false);
182 ASSERT_OK(load_bpf_testmod(false), "restore bpf_testmod");
183 end_mmap:
184 munmap(fault_addr, 4096);
185 atomic_store(&state, _TS_INVALID);
186 }
187
188 static const struct test_config ksym_config = {
189 .str_open = "ksym_race__open_and_load",
190 .bpf_open_and_load = (void *)ksym_race__open_and_load,
191 .bpf_destroy = (void *)ksym_race__destroy,
192 };
193
194 static const struct test_config kfunc_config = {
195 .str_open = "kfunc_call_race__open_and_load",
196 .bpf_open_and_load = (void *)kfunc_call_race__open_and_load,
197 .bpf_destroy = (void *)kfunc_call_race__destroy,
198 };
199
200 void serial_test_bpf_mod_race(void)
201 {
202 if (test__start_subtest("ksym (used_btfs UAF)"))
203 test_bpf_mod_race_config(&ksym_config);
204 if (test__start_subtest("kfunc (kfunc_btf_tab UAF)"))
205 test_bpf_mod_race_config(&kfunc_config);
206 }
207
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