2 * ldt_gdt.c - Test cases for LDT and GDT access
3 * Copyright (c) 2015 Andrew Lutomirski
16 #include <sys/syscall.h>
18 #include <sys/types.h>
23 #include <linux/futex.h>
25 #define AR_ACCESSED (1<<8)
27 #define AR_TYPE_RODATA (0 * (1<<9))
28 #define AR_TYPE_RWDATA (1 * (1<<9))
29 #define AR_TYPE_RODATA_EXPDOWN (2 * (1<<9))
30 #define AR_TYPE_RWDATA_EXPDOWN (3 * (1<<9))
31 #define AR_TYPE_XOCODE (4 * (1<<9))
32 #define AR_TYPE_XRCODE (5 * (1<<9))
33 #define AR_TYPE_XOCODE_CONF (6 * (1<<9))
34 #define AR_TYPE_XRCODE_CONF (7 * (1<<9))
36 #define AR_DPL3 (3 * (1<<13))
38 #define AR_S (1 << 12)
39 #define AR_P (1 << 15)
40 #define AR_AVL (1 << 20)
41 #define AR_L (1 << 21)
42 #define AR_DB (1 << 22)
43 #define AR_G (1 << 23)
47 static void check_invalid_segment(uint16_t index, int ldt)
49 uint32_t has_limit = 0, has_ar = 0, limit, ar;
50 uint32_t selector = (index << 3) | (ldt << 2) | 3;
52 asm ("lsl %[selector], %[limit]\n\t"
54 "movl $1, %[has_limit]\n\t"
56 : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
57 : [selector] "r" (selector));
58 asm ("larl %[selector], %[ar]\n\t"
60 "movl $1, %[has_ar]\n\t"
62 : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
63 : [selector] "r" (selector));
65 if (has_limit || has_ar) {
66 printf("[FAIL]\t%s entry %hu is valid but should be invalid\n",
67 (ldt ? "LDT" : "GDT"), index);
70 printf("[OK]\t%s entry %hu is invalid\n",
71 (ldt ? "LDT" : "GDT"), index);
75 static void check_valid_segment(uint16_t index, int ldt,
76 uint32_t expected_ar, uint32_t expected_limit,
79 uint32_t has_limit = 0, has_ar = 0, limit, ar;
80 uint32_t selector = (index << 3) | (ldt << 2) | 3;
82 asm ("lsl %[selector], %[limit]\n\t"
84 "movl $1, %[has_limit]\n\t"
86 : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
87 : [selector] "r" (selector));
88 asm ("larl %[selector], %[ar]\n\t"
90 "movl $1, %[has_ar]\n\t"
92 : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
93 : [selector] "r" (selector));
95 if (!has_limit || !has_ar) {
96 printf("[FAIL]\t%s entry %hu is invalid but should be valid\n",
97 (ldt ? "LDT" : "GDT"), index);
102 if (ar != expected_ar) {
103 printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n",
104 (ldt ? "LDT" : "GDT"), index, ar, expected_ar);
106 } else if (limit != expected_limit) {
107 printf("[FAIL]\t%s entry %hu has limit 0x%08X but expected 0x%08X\n",
108 (ldt ? "LDT" : "GDT"), index, limit, expected_limit);
110 } else if (verbose) {
111 printf("[OK]\t%s entry %hu has AR 0x%08X and limit 0x%08X\n",
112 (ldt ? "LDT" : "GDT"), index, ar, limit);
116 static bool install_valid_mode(const struct user_desc *desc, uint32_t ar,
119 int ret = syscall(SYS_modify_ldt, oldmode ? 1 : 0x11,
120 desc, sizeof(*desc));
124 uint32_t limit = desc->limit;
125 if (desc->limit_in_pages)
126 limit = (limit << 12) + 4095;
127 check_valid_segment(desc->entry_number, 1, ar, limit, true);
129 } else if (errno == ENOSYS) {
130 printf("[OK]\tmodify_ldt returned -ENOSYS\n");
133 if (desc->seg_32bit) {
134 printf("[FAIL]\tUnexpected modify_ldt failure %d\n",
139 printf("[OK]\tmodify_ldt rejected 16 bit segment\n");
145 static bool install_valid(const struct user_desc *desc, uint32_t ar)
147 return install_valid_mode(desc, ar, false);
150 static void install_invalid(const struct user_desc *desc, bool oldmode)
152 int ret = syscall(SYS_modify_ldt, oldmode ? 1 : 0x11,
153 desc, sizeof(*desc));
157 check_invalid_segment(desc->entry_number, 1);
158 } else if (errno == ENOSYS) {
159 printf("[OK]\tmodify_ldt returned -ENOSYS\n");
161 if (desc->seg_32bit) {
162 printf("[FAIL]\tUnexpected modify_ldt failure %d\n",
166 printf("[OK]\tmodify_ldt rejected 16 bit segment\n");
171 static int safe_modify_ldt(int func, struct user_desc *ptr,
172 unsigned long bytecount)
174 int ret = syscall(SYS_modify_ldt, 0x11, ptr, bytecount);
180 static void fail_install(struct user_desc *desc)
182 if (safe_modify_ldt(0x11, desc, sizeof(*desc)) == 0) {
183 printf("[FAIL]\tmodify_ldt accepted a bad descriptor\n");
185 } else if (errno == ENOSYS) {
186 printf("[OK]\tmodify_ldt returned -ENOSYS\n");
188 printf("[OK]\tmodify_ldt failure %d\n", errno);
192 static void do_simple_tests(void)
194 struct user_desc desc = {
199 .contents = 2, /* Code, not conforming */
202 .seg_not_present = 0,
205 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB);
207 desc.limit_in_pages = 1;
208 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
209 AR_S | AR_P | AR_DB | AR_G);
211 check_invalid_segment(1, 1);
213 desc.entry_number = 2;
214 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
215 AR_S | AR_P | AR_DB | AR_G);
217 check_invalid_segment(1, 1);
219 desc.base_addr = 0xf0000000;
220 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
221 AR_S | AR_P | AR_DB | AR_G);
224 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
225 AR_S | AR_P | AR_DB | AR_G | AR_AVL);
227 desc.seg_not_present = 1;
228 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
229 AR_S | AR_DB | AR_G | AR_AVL);
232 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
233 AR_S | AR_G | AR_AVL);
237 install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA |
238 AR_S | AR_DB | AR_G | AR_AVL);
240 desc.read_exec_only = 1;
241 install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA |
242 AR_S | AR_DB | AR_G | AR_AVL);
245 install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA_EXPDOWN |
246 AR_S | AR_DB | AR_G | AR_AVL);
248 desc.read_exec_only = 0;
249 desc.limit_in_pages = 0;
250 install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA_EXPDOWN |
251 AR_S | AR_DB | AR_AVL);
254 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE_CONF |
255 AR_S | AR_DB | AR_AVL);
257 desc.read_exec_only = 1;
258 install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE_CONF |
259 AR_S | AR_DB | AR_AVL);
261 desc.read_exec_only = 0;
263 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
264 AR_S | AR_DB | AR_AVL);
266 desc.read_exec_only = 1;
270 install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE |
271 AR_S | AR_DB | AR_AVL);
275 bool entry1_okay = install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE |
276 AR_S | AR_DB | AR_AVL);
279 printf("[RUN]\tTest fork\n");
280 pid_t child = fork();
283 check_valid_segment(desc.entry_number, 1,
284 AR_DPL3 | AR_TYPE_XOCODE |
285 AR_S | AR_DB | AR_AVL, desc.limit,
287 check_invalid_segment(1, 1);
291 if (waitpid(child, &status, 0) != child ||
292 !WIFEXITED(status)) {
293 printf("[FAIL]\tChild died\n");
295 } else if (WEXITSTATUS(status) != 0) {
296 printf("[FAIL]\tChild failed\n");
299 printf("[OK]\tChild succeeded\n");
303 printf("[RUN]\tTest size\n");
305 for (i = 0; i < 8192; i++) {
306 desc.entry_number = i;
308 if (safe_modify_ldt(0x11, &desc, sizeof(desc)) != 0) {
309 printf("[FAIL]\tFailed to install entry %d\n", i);
314 for (int j = 0; j < i; j++) {
315 check_valid_segment(j, 1, AR_DPL3 | AR_TYPE_XOCODE |
316 AR_S | AR_DB | AR_AVL, j, false);
318 printf("[DONE]\tSize test\n");
320 printf("[SKIP]\tSkipping fork and size tests because we have no LDT\n");
323 /* Test entry_number too high. */
324 desc.entry_number = 8192;
327 /* Test deletion and actions mistakeable for deletion. */
328 memset(&desc, 0, sizeof(desc));
329 install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P);
331 desc.seg_not_present = 1;
332 install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S);
334 desc.seg_not_present = 0;
335 desc.read_exec_only = 1;
336 install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S | AR_P);
338 desc.read_exec_only = 0;
339 desc.seg_not_present = 1;
340 install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S);
342 desc.read_exec_only = 1;
344 install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S);
348 install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S);
351 install_invalid(&desc, false);
353 desc.seg_not_present = 0;
354 desc.read_exec_only = 0;
356 install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P | AR_DB);
357 install_invalid(&desc, true);
363 * 2: thread should clear LDT entry 0
364 * 3: thread should exit
366 static volatile unsigned int ftx;
368 static void *threadproc(void *ctx)
373 if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
374 err(1, "sched_setaffinity to CPU 1"); /* should never fail */
377 syscall(SYS_futex, &ftx, FUTEX_WAIT, 0, NULL, NULL, 0);
383 /* clear LDT entry 0 */
384 const struct user_desc desc = {};
385 if (syscall(SYS_modify_ldt, 1, &desc, sizeof(desc)) != 0)
386 err(1, "modify_ldt");
388 /* If ftx == 2, set it to zero. If ftx == 100, quit. */
390 asm volatile ("lock xaddl %[x], %[ftx]" :
391 [x] "+r" (x), [ftx] "+m" (ftx));
397 static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
401 memset(&sa, 0, sizeof(sa));
402 sa.sa_sigaction = handler;
403 sa.sa_flags = SA_SIGINFO | flags;
404 sigemptyset(&sa.sa_mask);
405 if (sigaction(sig, &sa, 0))
410 static jmp_buf jmpbuf;
412 static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
414 siglongjmp(jmpbuf, 1);
417 static void do_multicpu_tests(void)
421 int failures = 0, iters = 5, i;
422 unsigned short orig_ss;
426 if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0) {
427 printf("[SKIP]\tCannot set affinity to CPU 1\n");
433 if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0) {
434 printf("[SKIP]\tCannot set affinity to CPU 0\n");
438 sethandler(SIGSEGV, sigsegv, 0);
440 /* True 32-bit kernels send SIGILL instead of SIGSEGV on IRET faults. */
441 sethandler(SIGILL, sigsegv, 0);
444 printf("[RUN]\tCross-CPU LDT invalidation\n");
446 if (pthread_create(&thread, 0, threadproc, 0) != 0)
447 err(1, "pthread_create");
449 asm volatile ("mov %%ss, %0" : "=rm" (orig_ss));
451 for (i = 0; i < 5; i++) {
452 if (sigsetjmp(jmpbuf, 1) != 0)
455 /* Make sure the thread is ready after the last test. */
459 struct user_desc desc = {
464 .contents = 0, /* Data */
467 .seg_not_present = 0,
471 if (safe_modify_ldt(0x11, &desc, sizeof(desc)) != 0) {
473 err(1, "modify_ldt");
474 printf("[SKIP]\tmodify_ldt unavailable\n");
478 /* Arm the thread. */
480 syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
482 asm volatile ("mov %0, %%ss" : : "r" (0x7));
491 * On success, modify_ldt will segfault us synchronously,
492 * and we'll escape via siglongjmp.
496 asm volatile ("mov %0, %%ss" : : "rm" (orig_ss));
499 ftx = 100; /* Kill the thread. */
500 syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);
502 if (pthread_join(thread, NULL) != 0)
503 err(1, "pthread_join");
506 printf("[FAIL]\t%d of %d iterations failed\n", failures, iters);
509 printf("[OK]\tAll %d iterations succeeded\n", iters);
513 static int finish_exec_test(void)
516 * In a sensible world, this would be check_invalid_segment(0, 1);
517 * For better or for worse, though, the LDT is inherited across exec.
518 * We can probably change this safely, but for now we test it.
520 check_valid_segment(0, 1,
521 AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB,
524 return nerrs ? 1 : 0;
527 static void do_exec_test(void)
529 printf("[RUN]\tTest exec\n");
531 struct user_desc desc = {
536 .contents = 2, /* Code, not conforming */
539 .seg_not_present = 0,
542 install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB);
544 pid_t child = fork();
546 execl("/proc/self/exe", "ldt_gdt_test_exec", NULL);
547 printf("[FAIL]\tCould not exec self\n");
548 exit(1); /* exec failed */
551 if (waitpid(child, &status, 0) != child ||
552 !WIFEXITED(status)) {
553 printf("[FAIL]\tChild died\n");
555 } else if (WEXITSTATUS(status) != 0) {
556 printf("[FAIL]\tChild failed\n");
559 printf("[OK]\tChild succeeded\n");
564 int main(int argc, char **argv)
566 if (argc == 1 && !strcmp(argv[0], "ldt_gdt_test_exec"))
567 return finish_exec_test();
575 return nerrs ? 1 : 0;