kern_pax.c revision 1.18
1 /* $NetBSD: kern_pax.c,v 1.18 2007/12/26 22:11:51 christos Exp $ */ 2 3 /*- 4 * Copyright (c) 2006 Elad Efrat <elad (at) NetBSD.org> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. The name of the author may not be used to endorse or promote products 16 * derived from this software without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 19 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 20 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 21 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 22 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 23 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 27 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 */ 29 30 #include <sys/cdefs.h> 31 __KERNEL_RCSID(0, "$NetBSD: kern_pax.c,v 1.18 2007/12/26 22:11:51 christos Exp $"); 32 33 #include "opt_pax.h" 34 35 #include <sys/param.h> 36 #include <sys/proc.h> 37 #include <sys/exec_elf.h> 38 #include <sys/pax.h> 39 #include <sys/sysctl.h> 40 #include <sys/malloc.h> 41 #include <sys/fileassoc.h> 42 #include <sys/syslog.h> 43 #include <sys/vnode.h> 44 #include <sys/queue.h> 45 #include <sys/kauth.h> 46 47 #ifdef PAX_ASLR 48 #include <sys/mman.h> 49 #include <sys/rnd.h> 50 #include <sys/exec.h> 51 52 int pax_aslr_enabled = 1; 53 int pax_aslr_global = PAX_ASLR; 54 55 specificdata_key_t pax_aslr_key; 56 57 #ifndef PAX_ASLR_DELTA_MMAP_LSB 58 #define PAX_ASLR_DELTA_MMAP_LSB PGSHIFT 59 #endif 60 #ifndef PAX_ASLR_DELTA_MMAP_LEN 61 #define PAX_ASLR_DELTA_MMAP_LEN ((sizeof(void *) * NBBY) / 2) 62 #endif 63 #ifndef PAX_ASLR_DELTA_STACK_LSB 64 #define PAX_ASLR_DELTA_STACK_LSB PGSHIFT 65 #endif 66 #ifndef PAX_ASLR_DELTA_STACK_LEN 67 #define PAX_ASLR_DELTA_STACK_LEN 12 68 #endif 69 70 #endif /* PAX_ASLR */ 71 72 #ifdef PAX_MPROTECT 73 static int pax_mprotect_enabled = 1; 74 static int pax_mprotect_global = PAX_MPROTECT; 75 76 specificdata_key_t pax_mprotect_key; 77 #endif /* PAX_MPROTECT */ 78 79 #ifdef PAX_SEGVGUARD 80 #ifndef PAX_SEGVGUARD_EXPIRY 81 #define PAX_SEGVGUARD_EXPIRY (2 * 60) 82 #endif 83 84 #ifndef PAX_SEGVGUARD_SUSPENSION 85 #define PAX_SEGVGUARD_SUSPENSION (10 * 60) 86 #endif 87 88 #ifndef PAX_SEGVGUARD_MAXCRASHES 89 #define PAX_SEGVGUARD_MAXCRASHES 5 90 #endif 91 92 static int pax_segvguard_enabled = 1; 93 static int pax_segvguard_global = PAX_SEGVGUARD; 94 static int pax_segvguard_expiry = PAX_SEGVGUARD_EXPIRY; 95 static int pax_segvguard_suspension = PAX_SEGVGUARD_SUSPENSION; 96 static int pax_segvguard_maxcrashes = PAX_SEGVGUARD_MAXCRASHES; 97 98 static fileassoc_t segvguard_id; 99 specificdata_key_t pax_segvguard_key; 100 101 struct pax_segvguard_uid_entry { 102 uid_t sue_uid; 103 size_t sue_ncrashes; 104 time_t sue_expiry; 105 time_t sue_suspended; 106 LIST_ENTRY(pax_segvguard_uid_entry) sue_list; 107 }; 108 109 struct pax_segvguard_entry { 110 LIST_HEAD(, pax_segvguard_uid_entry) segv_uids; 111 }; 112 113 static void pax_segvguard_cb(void *); 114 #endif /* PAX_SEGVGUARD */ 115 116 /* PaX internal setspecific flags */ 117 #define PAX_MPROTECT_EXPLICIT_ENABLE (void *)0x01 118 #define PAX_MPROTECT_EXPLICIT_DISABLE (void *)0x02 119 #define PAX_SEGVGUARD_EXPLICIT_ENABLE (void *)0x03 120 #define PAX_SEGVGUARD_EXPLICIT_DISABLE (void *)0x04 121 #define PAX_ASLR_EXPLICIT_ENABLE (void *)0x05 122 #define PAX_ASLR_EXPLICIT_DISABLE (void *)0x06 123 124 SYSCTL_SETUP(sysctl_security_pax_setup, "sysctl security.pax setup") 125 { 126 const struct sysctlnode *rnode = NULL, *cnode; 127 128 sysctl_createv(clog, 0, NULL, &rnode, 129 CTLFLAG_PERMANENT, 130 CTLTYPE_NODE, "security", NULL, 131 NULL, 0, NULL, 0, 132 CTL_SECURITY, CTL_EOL); 133 134 sysctl_createv(clog, 0, &rnode, &rnode, 135 CTLFLAG_PERMANENT, 136 CTLTYPE_NODE, "pax", 137 SYSCTL_DESCR("PaX (exploit mitigation) features."), 138 NULL, 0, NULL, 0, 139 CTL_CREATE, CTL_EOL); 140 141 #ifdef PAX_MPROTECT 142 cnode = rnode; 143 sysctl_createv(clog, 0, &rnode, &rnode, 144 CTLFLAG_PERMANENT, 145 CTLTYPE_NODE, "mprotect", 146 SYSCTL_DESCR("mprotect(2) W^X restrictions."), 147 NULL, 0, NULL, 0, 148 CTL_CREATE, CTL_EOL); 149 sysctl_createv(clog, 0, &rnode, NULL, 150 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 151 CTLTYPE_INT, "enabled", 152 SYSCTL_DESCR("Restrictions enabled."), 153 NULL, 0, &pax_mprotect_enabled, 0, 154 CTL_CREATE, CTL_EOL); 155 sysctl_createv(clog, 0, &rnode, NULL, 156 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 157 CTLTYPE_INT, "global", 158 SYSCTL_DESCR("When enabled, unless explicitly " 159 "specified, apply restrictions to " 160 "all processes."), 161 NULL, 0, &pax_mprotect_global, 0, 162 CTL_CREATE, CTL_EOL); 163 #endif /* PAX_MPROTECT */ 164 165 #ifdef PAX_SEGVGUARD 166 rnode = cnode; 167 sysctl_createv(clog, 0, &rnode, &rnode, 168 CTLFLAG_PERMANENT, 169 CTLTYPE_NODE, "segvguard", 170 SYSCTL_DESCR("PaX segvguard."), 171 NULL, 0, NULL, 0, 172 CTL_CREATE, CTL_EOL); 173 sysctl_createv(clog, 0, &rnode, NULL, 174 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 175 CTLTYPE_INT, "enabled", 176 SYSCTL_DESCR("segvguard enabled."), 177 NULL, 0, &pax_segvguard_enabled, 0, 178 CTL_CREATE, CTL_EOL); 179 sysctl_createv(clog, 0, &rnode, NULL, 180 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 181 CTLTYPE_INT, "global", 182 SYSCTL_DESCR("segvguard all programs."), 183 NULL, 0, &pax_segvguard_global, 0, 184 CTL_CREATE, CTL_EOL); 185 sysctl_createv(clog, 0, &rnode, NULL, 186 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 187 CTLTYPE_INT, "expiry_timeout", 188 SYSCTL_DESCR("Entry expiry timeout (in seconds)."), 189 NULL, 0, &pax_segvguard_expiry, 0, 190 CTL_CREATE, CTL_EOL); 191 sysctl_createv(clog, 0, &rnode, NULL, 192 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 193 CTLTYPE_INT, "suspend_timeout", 194 SYSCTL_DESCR("Entry suspension timeout (in seconds)."), 195 NULL, 0, &pax_segvguard_suspension, 0, 196 CTL_CREATE, CTL_EOL); 197 sysctl_createv(clog, 0, &rnode, NULL, 198 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 199 CTLTYPE_INT, "max_crashes", 200 SYSCTL_DESCR("Max number of crashes before expiry."), 201 NULL, 0, &pax_segvguard_maxcrashes, 0, 202 CTL_CREATE, CTL_EOL); 203 #endif /* PAX_SEGVGUARD */ 204 205 #ifdef PAX_ASLR 206 rnode = cnode; 207 sysctl_createv(clog, 0, &rnode, &rnode, 208 CTLFLAG_PERMANENT, 209 CTLTYPE_NODE, "aslr", 210 SYSCTL_DESCR("Address Space Layout Randomization."), 211 NULL, 0, NULL, 0, 212 CTL_CREATE, CTL_EOL); 213 sysctl_createv(clog, 0, &rnode, NULL, 214 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 215 CTLTYPE_INT, "enabled", 216 SYSCTL_DESCR("Restrictions enabled."), 217 NULL, 0, &pax_aslr_enabled, 0, 218 CTL_CREATE, CTL_EOL); 219 sysctl_createv(clog, 0, &rnode, NULL, 220 CTLFLAG_PERMANENT|CTLFLAG_READWRITE, 221 CTLTYPE_INT, "global", 222 SYSCTL_DESCR("When enabled, unless explicitly " 223 "specified, apply to all processes."), 224 NULL, 0, &pax_aslr_global, 0, 225 CTL_CREATE, CTL_EOL); 226 sysctl_createv(clog, 0, &rnode, NULL, 227 CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE, 228 CTLTYPE_INT, "mmap_len", 229 SYSCTL_DESCR("Number of bits randomized for " 230 "mmap(2) calls."), 231 NULL, PAX_ASLR_DELTA_MMAP_LEN, NULL, 0, 232 CTL_CREATE, CTL_EOL); 233 #endif /* PAX_ASLR */ 234 } 235 236 /* 237 * Initialize PaX. 238 */ 239 void 240 pax_init(void) 241 { 242 #ifdef PAX_SEGVGUARD 243 int error; 244 #endif /* PAX_SEGVGUARD */ 245 246 #ifdef PAX_ASLR 247 proc_specific_key_create(&pax_aslr_key, NULL); 248 #endif /* PAX_ASLR */ 249 250 #ifdef PAX_MPROTECT 251 proc_specific_key_create(&pax_mprotect_key, NULL); 252 #endif /* PAX_MPROTECT */ 253 254 #ifdef PAX_SEGVGUARD 255 error = fileassoc_register("segvguard", pax_segvguard_cb, 256 &segvguard_id); 257 if (error) { 258 panic("pax_init: segvguard_id: error=%d\n", error); 259 } 260 proc_specific_key_create(&pax_segvguard_key, NULL); 261 #endif /* PAX_SEGVGUARD */ 262 } 263 264 void 265 pax_adjust(struct lwp *l, uint32_t f) 266 { 267 #ifdef PAX_MPROTECT 268 if (pax_mprotect_enabled) { 269 if (f & ELF_NOTE_PAX_MPROTECT) 270 proc_setspecific(l->l_proc, pax_mprotect_key, 271 PAX_MPROTECT_EXPLICIT_ENABLE); 272 if (f & ELF_NOTE_PAX_NOMPROTECT) 273 proc_setspecific(l->l_proc, pax_mprotect_key, 274 PAX_MPROTECT_EXPLICIT_DISABLE); 275 } 276 #endif /* PAX_MPROTECT */ 277 278 #ifdef PAX_SEGVGUARD 279 if (pax_segvguard_enabled) { 280 if (f & ELF_NOTE_PAX_GUARD) 281 proc_setspecific(l->l_proc, pax_segvguard_key, 282 PAX_SEGVGUARD_EXPLICIT_ENABLE); 283 if (f & ELF_NOTE_PAX_NOGUARD) 284 proc_setspecific(l->l_proc, pax_segvguard_key, 285 PAX_SEGVGUARD_EXPLICIT_DISABLE); 286 } 287 #endif /* PAX_SEGVGUARD */ 288 289 #ifdef PAX_ASLR 290 if (pax_aslr_enabled) { 291 if (f & ELF_NOTE_PAX_ASLR) 292 proc_setspecific(l->l_proc, pax_aslr_key, 293 PAX_ASLR_EXPLICIT_ENABLE); 294 if (f & ELF_NOTE_PAX_NOASLR) 295 proc_setspecific(l->l_proc, pax_aslr_key, 296 PAX_ASLR_EXPLICIT_DISABLE); 297 } 298 #endif /* PAX_ASLR */ 299 } 300 301 #ifdef PAX_MPROTECT 302 void 303 pax_mprotect(struct lwp *l, vm_prot_t *prot, vm_prot_t *maxprot) 304 { 305 void *t; 306 307 if (!pax_mprotect_enabled) 308 return; 309 310 t = proc_getspecific(l->l_proc, pax_mprotect_key); 311 if ((pax_mprotect_global && t == PAX_MPROTECT_EXPLICIT_DISABLE) || 312 (!pax_mprotect_global && t != PAX_MPROTECT_EXPLICIT_ENABLE)) 313 return; 314 315 if ((*prot & (VM_PROT_WRITE|VM_PROT_EXECUTE)) != VM_PROT_EXECUTE) { 316 *prot &= ~VM_PROT_EXECUTE; 317 *maxprot &= ~VM_PROT_EXECUTE; 318 } else { 319 *prot &= ~VM_PROT_WRITE; 320 *maxprot &= ~VM_PROT_WRITE; 321 } 322 } 323 #endif /* PAX_MPROTECT */ 324 325 #ifdef PAX_ASLR 326 bool 327 pax_aslr_active(struct lwp *l) 328 { 329 void *t; 330 if (!pax_aslr_enabled) 331 return false; 332 333 t = proc_getspecific(l->l_proc, pax_aslr_key); 334 if ((pax_aslr_global && t == PAX_ASLR_EXPLICIT_DISABLE) || 335 (!pax_aslr_global && t != PAX_ASLR_EXPLICIT_ENABLE)) 336 return false; 337 return true; 338 } 339 340 void 341 pax_aslr_init(struct lwp *l, struct vmspace *vm) 342 { 343 if (!pax_aslr_active(l)) 344 return; 345 346 vm->vm_aslr_delta_mmap = PAX_ASLR_DELTA(arc4random(), 347 PAX_ASLR_DELTA_MMAP_LSB, PAX_ASLR_DELTA_MMAP_LEN); 348 } 349 350 void 351 pax_aslr(struct lwp *l, vaddr_t *addr, vaddr_t orig_addr, int f) 352 { 353 if (!pax_aslr_active(l)) 354 return; 355 356 if (!(f & MAP_FIXED) && ((orig_addr == 0) || !(f & MAP_ANON))) { 357 #ifdef DEBUG_ASLR 358 uprintf("applying to 0x%lx orig_addr=0x%lx f=%x\n", 359 (unsigned long)*addr, (unsigned long)orig_addr, f); 360 #endif 361 if (!(l->l_proc->p_vmspace->vm_map.flags & VM_MAP_TOPDOWN)) 362 *addr += l->l_proc->p_vmspace->vm_aslr_delta_mmap; 363 else 364 *addr -= l->l_proc->p_vmspace->vm_aslr_delta_mmap; 365 #ifdef DEBUG_ASLR 366 uprintf("result 0x%lx\n", *addr); 367 #endif 368 } 369 #ifdef DEBUG_ASLR 370 else 371 uprintf("not applying to 0x%lx orig_addr=0x%lx f=%x\n", 372 (unsigned long)*addr, (unsigned long)orig_addr, f); 373 #endif 374 } 375 376 void 377 pax_aslr_stack(struct lwp *l, struct exec_package *epp, u_long *max_stack_size) 378 { 379 if (pax_aslr_active(l)) { 380 u_long d = PAX_ASLR_DELTA(epp->ep_random, 381 PAX_ASLR_DELTA_STACK_LSB, 382 PAX_ASLR_DELTA_STACK_LEN); 383 #ifdef DEBUG_ASLR 384 uprintf("stack 0x%lx d=0x%lx 0x%lx\n", 385 epp->ep_minsaddr, d, epp->ep_minsaddr - d); 386 #endif 387 epp->ep_minsaddr -= d; 388 *max_stack_size -= d; 389 } 390 } 391 #endif /* PAX_ASLR */ 392 393 #ifdef PAX_SEGVGUARD 394 static void 395 pax_segvguard_cb(void *v) 396 { 397 struct pax_segvguard_entry *p; 398 struct pax_segvguard_uid_entry *up; 399 400 if (v == NULL) 401 return; 402 403 p = v; 404 while ((up = LIST_FIRST(&p->segv_uids)) != NULL) { 405 LIST_REMOVE(up, sue_list); 406 free(up, M_TEMP); 407 } 408 409 free(v, M_TEMP); 410 } 411 412 /* 413 * Called when a process of image vp generated a segfault. 414 */ 415 int 416 pax_segvguard(struct lwp *l, struct vnode *vp, const char *name, 417 bool crashed) 418 { 419 struct pax_segvguard_entry *p; 420 struct pax_segvguard_uid_entry *up; 421 struct timeval tv; 422 uid_t uid; 423 void *t; 424 bool have_uid; 425 426 if (!pax_segvguard_enabled) 427 return (0); 428 429 t = proc_getspecific(l->l_proc, pax_segvguard_key); 430 if ((pax_segvguard_global && t == PAX_SEGVGUARD_EXPLICIT_DISABLE) || 431 (!pax_segvguard_global && t != PAX_SEGVGUARD_EXPLICIT_ENABLE)) 432 return (0); 433 434 if (vp == NULL) 435 return (EFAULT); 436 437 /* Check if we already monitor the file. */ 438 p = fileassoc_lookup(vp, segvguard_id); 439 440 /* Fast-path if starting a program we don't know. */ 441 if (p == NULL && !crashed) 442 return (0); 443 444 microtime(&tv); 445 446 /* 447 * If a program we don't know crashed, we need to create a new entry 448 * for it. 449 */ 450 if (p == NULL) { 451 p = malloc(sizeof(*p), M_TEMP, M_WAITOK); 452 fileassoc_add(vp, segvguard_id, p); 453 LIST_INIT(&p->segv_uids); 454 455 /* 456 * Initialize a new entry with "crashes so far" of 1. 457 * The expiry time is when we purge the entry if it didn't 458 * reach the limit. 459 */ 460 up = malloc(sizeof(*up), M_TEMP, M_WAITOK); 461 up->sue_uid = kauth_cred_getuid(l->l_cred); 462 up->sue_ncrashes = 1; 463 up->sue_expiry = tv.tv_sec + pax_segvguard_expiry; 464 up->sue_suspended = 0; 465 466 LIST_INSERT_HEAD(&p->segv_uids, up, sue_list); 467 468 return (0); 469 } 470 471 /* 472 * A program we "know" either executed or crashed again. 473 * See if it's a culprit we're familiar with. 474 */ 475 uid = kauth_cred_getuid(l->l_cred); 476 have_uid = false; 477 LIST_FOREACH(up, &p->segv_uids, sue_list) { 478 if (up->sue_uid == uid) { 479 have_uid = true; 480 break; 481 } 482 } 483 484 /* 485 * It's someone else. Add an entry for him if we crashed. 486 */ 487 if (!have_uid) { 488 if (crashed) { 489 up = malloc(sizeof(*up), M_TEMP, M_WAITOK); 490 up->sue_uid = uid; 491 up->sue_ncrashes = 1; 492 up->sue_expiry = tv.tv_sec + pax_segvguard_expiry; 493 up->sue_suspended = 0; 494 495 LIST_INSERT_HEAD(&p->segv_uids, up, sue_list); 496 } 497 498 return (0); 499 } 500 501 if (crashed) { 502 /* Check if timer on previous crashes expired first. */ 503 if (up->sue_expiry < tv.tv_sec) { 504 log(LOG_INFO, "PaX Segvguard: [%s] Suspension" 505 " expired.\n", name ? name : "unknown"); 506 507 up->sue_ncrashes = 1; 508 up->sue_expiry = tv.tv_sec + pax_segvguard_expiry; 509 up->sue_suspended = 0; 510 511 return (0); 512 } 513 514 up->sue_ncrashes++; 515 516 if (up->sue_ncrashes >= pax_segvguard_maxcrashes) { 517 log(LOG_ALERT, "PaX Segvguard: [%s] Suspending " 518 "execution for %d seconds after %zu crashes.\n", 519 name ? name : "unknown", pax_segvguard_suspension, 520 up->sue_ncrashes); 521 522 /* Suspend this program for a while. */ 523 up->sue_suspended = tv.tv_sec + pax_segvguard_suspension; 524 up->sue_ncrashes = 0; 525 up->sue_expiry = 0; 526 } 527 } else { 528 /* Are we supposed to be suspended? */ 529 if (up->sue_suspended > tv.tv_sec) { 530 log(LOG_ALERT, "PaX Segvguard: [%s] Preventing " 531 "execution due to repeated segfaults.\n", name ? 532 name : "unknown"); 533 534 return (EPERM); 535 } 536 } 537 538 return (0); 539 } 540 #endif /* PAX_SEGVGUARD */ 541
Indexes created Tue Sep 30 11:09:46 GMT 2025