1 /* $NetBSD: kern_pax.c,v 1.63 2022/10/26 23:22:38 riastradh Exp $ */
2
3 /*
4 * Copyright (c) 2015, 2020 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Maxime Villard.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32 /*
33 * Copyright (c) 2006 Elad Efrat <elad@NetBSD.org>
34 * All rights reserved.
35 *
36 * Redistribution and use in source and binary forms, with or without
37 * modification, are permitted provided that the following conditions
38 * are met:
39 * 1. Redistributions of source code must retain the above copyright
40 * notice, this list of conditions and the following disclaimer.
41 * 2. Redistributions in binary form must reproduce the above copyright
42 * notice, this list of conditions and the following disclaimer in the
43 * documentation and/or other materials provided with the distribution.
44 * 3. The name of the author may not be used to endorse or promote products
45 * derived from this software without specific prior written permission.
46 *
47 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
48 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
49 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
50 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
51 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
52 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
53 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
54 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
55 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
56 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
57 */
58
59 #include <sys/cdefs.h>
60 __KERNEL_RCSID(0, "$NetBSD: kern_pax.c,v 1.63 2022/10/26 23:22:38 riastradh Exp $");
61
62 #include "opt_pax.h"
63
64 #include <sys/param.h>
65 #include <sys/proc.h>
66 #include <sys/exec.h>
67 #include <sys/exec_elf.h>
68 #include <sys/pax.h>
69 #include <sys/sysctl.h>
70 #include <sys/kmem.h>
71 #include <sys/mman.h>
72 #include <sys/syslog.h>
73 #include <sys/vnode.h>
74 #include <sys/queue.h>
75 #include <sys/bitops.h>
76 #include <sys/kauth.h>
77 #include <sys/cprng.h>
78
79 #ifdef PAX_ASLR_DEBUG
80 #define PAX_DPRINTF(_fmt, args...) \
81 do if (pax_aslr_debug) uprintf("%s: " _fmt "\n", __func__, ##args); \
82 while (/*CONSTCOND*/0)
83 #else
84 #define PAX_DPRINTF(_fmt, args...) do {} while (/*CONSTCOND*/0)
85 #endif
86
87 #ifdef PAX_ASLR
88 #include <sys/mman.h>
89 #include <sys/resourcevar.h>
90
91 int pax_aslr_enabled = 1;
92 int pax_aslr_global = PAX_ASLR;
93
94 #ifndef PAX_ASLR_DELTA_MMAP_LSB
95 #define PAX_ASLR_DELTA_MMAP_LSB PGSHIFT
96 #endif
97 #ifndef PAX_ASLR_DELTA_MMAP_LEN
98 #define PAX_ASLR_DELTA_MMAP_LEN ((sizeof(void *) * NBBY) / 2)
99 #endif
100 #ifndef PAX_ASLR_DELTA_MMAP_LEN32
101 #define PAX_ASLR_DELTA_MMAP_LEN32 ((sizeof(uint32_t) * NBBY) / 2)
102 #endif
103 #ifndef PAX_ASLR_DELTA_STACK_LSB
104 #define PAX_ASLR_DELTA_STACK_LSB PGSHIFT
105 #endif
106 #ifndef PAX_ASLR_DELTA_STACK_LEN
107 #define PAX_ASLR_DELTA_STACK_LEN ((sizeof(void *) * NBBY) / 4)
108 #endif
109 #ifndef PAX_ASLR_DELTA_STACK_LEN32
110 #define PAX_ASLR_DELTA_STACK_LEN32 ((sizeof(uint32_t) * NBBY) / 4)
111 #endif
112 #define PAX_ASLR_MAX_STACK_WASTE 8
113
114 #ifdef PAX_ASLR_DEBUG
115 int pax_aslr_debug;
116 /* flag set means disable */
117 int pax_aslr_flags;
118 uint32_t pax_aslr_rand;
119 #define PAX_ASLR_STACK 0x01
120 #define PAX_ASLR_STACK_GAP 0x02
121 #define PAX_ASLR_MMAP 0x04
122 #define PAX_ASLR_EXEC_OFFSET 0x08
123 #define PAX_ASLR_RTLD_OFFSET 0x10
124 #define PAX_ASLR_FIXED 0x20
125 #endif
126
127 static bool pax_aslr_elf_flags_active(uint32_t);
128 #endif /* PAX_ASLR */
129
130 #ifdef PAX_MPROTECT
131 static int pax_mprotect_enabled = 1;
132 static int pax_mprotect_global = PAX_MPROTECT;
133 static int pax_mprotect_ptrace = 1;
134 static bool pax_mprotect_elf_flags_active(uint32_t);
135 #endif /* PAX_MPROTECT */
136 #ifdef PAX_MPROTECT_DEBUG
137 int pax_mprotect_debug;
138 #endif
139
140 #ifdef PAX_SEGVGUARD
141 #ifndef PAX_SEGVGUARD_EXPIRY
142 #define PAX_SEGVGUARD_EXPIRY (2 * 60)
143 #endif
144 #ifndef PAX_SEGVGUARD_SUSPENSION
145 #define PAX_SEGVGUARD_SUSPENSION (10 * 60)
146 #endif
147 #ifndef PAX_SEGVGUARD_MAXCRASHES
148 #define PAX_SEGVGUARD_MAXCRASHES 5
149 #endif
150
151
152 static int pax_segvguard_enabled = 1;
153 static int pax_segvguard_global = PAX_SEGVGUARD;
154 static int pax_segvguard_expiry = PAX_SEGVGUARD_EXPIRY;
155 static int pax_segvguard_suspension = PAX_SEGVGUARD_SUSPENSION;
156 static int pax_segvguard_maxcrashes = PAX_SEGVGUARD_MAXCRASHES;
157
158 struct pax_segvguard_uid_entry {
159 uid_t sue_uid;
160 size_t sue_ncrashes;
161 time_t sue_expiry;
162 time_t sue_suspended;
163 LIST_ENTRY(pax_segvguard_uid_entry) sue_list;
164 };
165
166 struct pax_segvguard_entry {
167 LIST_HEAD(, pax_segvguard_uid_entry) segv_uids;
168 };
169
170 static bool pax_segvguard_elf_flags_active(uint32_t);
171 #endif /* PAX_SEGVGUARD */
172
173 SYSCTL_SETUP(sysctl_security_pax_setup, "sysctl security.pax setup")
174 {
175 const struct sysctlnode *rnode = NULL, *cnode;
176
177 sysctl_createv(clog, 0, NULL, &rnode,
178 CTLFLAG_PERMANENT,
179 CTLTYPE_NODE, "pax",
180 SYSCTL_DESCR("PaX (exploit mitigation) features."),
181 NULL, 0, NULL, 0,
182 CTL_SECURITY, CTL_CREATE, CTL_EOL);
183
184 cnode = rnode;
185
186 #ifdef PAX_MPROTECT
187 rnode = cnode;
188 sysctl_createv(clog, 0, &rnode, &rnode,
189 CTLFLAG_PERMANENT,
190 CTLTYPE_NODE, "mprotect",
191 SYSCTL_DESCR("mprotect(2) W^X restrictions."),
192 NULL, 0, NULL, 0,
193 CTL_CREATE, CTL_EOL);
194 sysctl_createv(clog, 0, &rnode, NULL,
195 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
196 CTLTYPE_INT, "enabled",
197 SYSCTL_DESCR("Restrictions enabled."),
198 NULL, 0, &pax_mprotect_enabled, 0,
199 CTL_CREATE, CTL_EOL);
200 sysctl_createv(clog, 0, &rnode, NULL,
201 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
202 CTLTYPE_INT, "global",
203 SYSCTL_DESCR("When enabled, unless explicitly "
204 "specified, apply restrictions to "
205 "all processes."),
206 NULL, 0, &pax_mprotect_global, 0,
207 CTL_CREATE, CTL_EOL);
208 sysctl_createv(clog, 0, &rnode, NULL,
209 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
210 CTLTYPE_INT, "ptrace",
211 SYSCTL_DESCR("When enabled, allow ptrace(2) to "
212 "override mprotect permissions on traced "
213 "processes"),
214 NULL, 0, &pax_mprotect_ptrace, 0,
215 CTL_CREATE, CTL_EOL);
216 #ifdef PAX_MPROTECT_DEBUG
217 sysctl_createv(clog, 0, &rnode, NULL,
218 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
219 CTLTYPE_INT, "debug",
220 SYSCTL_DESCR("print mprotect changes."),
221 NULL, 0, &pax_mprotect_debug, 0,
222 CTL_CREATE, CTL_EOL);
223 #endif
224 #endif /* PAX_MPROTECT */
225
226 #ifdef PAX_SEGVGUARD
227 rnode = cnode;
228 sysctl_createv(clog, 0, &rnode, &rnode,
229 CTLFLAG_PERMANENT,
230 CTLTYPE_NODE, "segvguard",
231 SYSCTL_DESCR("PaX segvguard."),
232 NULL, 0, NULL, 0,
233 CTL_CREATE, CTL_EOL);
234 sysctl_createv(clog, 0, &rnode, NULL,
235 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
236 CTLTYPE_INT, "enabled",
237 SYSCTL_DESCR("segvguard enabled."),
238 NULL, 0, &pax_segvguard_enabled, 0,
239 CTL_CREATE, CTL_EOL);
240 sysctl_createv(clog, 0, &rnode, NULL,
241 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
242 CTLTYPE_INT, "global",
243 SYSCTL_DESCR("segvguard all programs."),
244 NULL, 0, &pax_segvguard_global, 0,
245 CTL_CREATE, CTL_EOL);
246 sysctl_createv(clog, 0, &rnode, NULL,
247 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
248 CTLTYPE_INT, "expiry_timeout",
249 SYSCTL_DESCR("Entry expiry timeout (in seconds)."),
250 NULL, 0, &pax_segvguard_expiry, 0,
251 CTL_CREATE, CTL_EOL);
252 sysctl_createv(clog, 0, &rnode, NULL,
253 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
254 CTLTYPE_INT, "suspend_timeout",
255 SYSCTL_DESCR("Entry suspension timeout (in seconds)."),
256 NULL, 0, &pax_segvguard_suspension, 0,
257 CTL_CREATE, CTL_EOL);
258 sysctl_createv(clog, 0, &rnode, NULL,
259 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
260 CTLTYPE_INT, "max_crashes",
261 SYSCTL_DESCR("Max number of crashes before expiry."),
262 NULL, 0, &pax_segvguard_maxcrashes, 0,
263 CTL_CREATE, CTL_EOL);
264 #endif /* PAX_SEGVGUARD */
265
266 #ifdef PAX_ASLR
267 rnode = cnode;
268 sysctl_createv(clog, 0, &rnode, &rnode,
269 CTLFLAG_PERMANENT,
270 CTLTYPE_NODE, "aslr",
271 SYSCTL_DESCR("Address Space Layout Randomization."),
272 NULL, 0, NULL, 0,
273 CTL_CREATE, CTL_EOL);
274 sysctl_createv(clog, 0, &rnode, NULL,
275 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
276 CTLTYPE_INT, "enabled",
277 SYSCTL_DESCR("Restrictions enabled."),
278 NULL, 0, &pax_aslr_enabled, 0,
279 CTL_CREATE, CTL_EOL);
280 sysctl_createv(clog, 0, &rnode, NULL,
281 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
282 CTLTYPE_INT, "global",
283 SYSCTL_DESCR("When enabled, unless explicitly "
284 "specified, apply to all processes."),
285 NULL, 0, &pax_aslr_global, 0,
286 CTL_CREATE, CTL_EOL);
287 #ifdef PAX_ASLR_DEBUG
288 sysctl_createv(clog, 0, &rnode, NULL,
289 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
290 CTLTYPE_INT, "debug",
291 SYSCTL_DESCR("Print ASLR selected addresses."),
292 NULL, 0, &pax_aslr_debug, 0,
293 CTL_CREATE, CTL_EOL);
294 sysctl_createv(clog, 0, &rnode, NULL,
295 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
296 CTLTYPE_INT, "flags",
297 SYSCTL_DESCR("Disable/Enable select ASLR features."),
298 NULL, 0, &pax_aslr_flags, 0,
299 CTL_CREATE, CTL_EOL);
300 sysctl_createv(clog, 0, &rnode, NULL,
301 CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
302 CTLTYPE_INT, "rand",
303 SYSCTL_DESCR("Use the given fixed random value"),
304 NULL, 0, &pax_aslr_rand, 0,
305 CTL_CREATE, CTL_EOL);
306 #endif
307 sysctl_createv(clog, 0, &rnode, NULL,
308 CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
309 CTLTYPE_INT, "mmap_len",
310 SYSCTL_DESCR("Number of bits randomized for "
311 "mmap(2) calls."),
312 NULL, PAX_ASLR_DELTA_MMAP_LEN, NULL, 0,
313 CTL_CREATE, CTL_EOL);
314 sysctl_createv(clog, 0, &rnode, NULL,
315 CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
316 CTLTYPE_INT, "stack_len",
317 SYSCTL_DESCR("Number of bits randomized for "
318 "the stack."),
319 NULL, PAX_ASLR_DELTA_STACK_LEN, NULL, 0,
320 CTL_CREATE, CTL_EOL);
321 sysctl_createv(clog, 0, &rnode, NULL,
322 CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
323 CTLTYPE_INT, "exec_len",
324 SYSCTL_DESCR("Number of bits randomized for "
325 "the PIE exec base."),
326 NULL, PAX_ASLR_DELTA_EXEC_LEN, NULL, 0,
327 CTL_CREATE, CTL_EOL);
328
329 #endif /* PAX_ASLR */
330 }
331
332 /*
333 * Initialize PaX.
334 */
335 void
pax_init(void)336 pax_init(void)
337 {
338 #ifdef PAX_ASLR
339 /* Adjust maximum stack by the size we can consume for ASLR */
340 maxsmap = MAXSSIZ - (MAXSSIZ / PAX_ASLR_MAX_STACK_WASTE);
341 // XXX: compat32 is not handled.
342 #endif
343 }
344
345 void
pax_set_flags(struct exec_package * epp,struct proc * p)346 pax_set_flags(struct exec_package *epp, struct proc *p)
347 {
348 p->p_pax = epp->ep_pax_flags;
349
350 #ifdef PAX_MPROTECT
351 if (pax_mprotect_ptrace == 0)
352 return;
353 /*
354 * If we are running under the debugger, turn off MPROTECT so
355 * the debugger can insert/delete breakpoints
356 */
357 if (p->p_slflag & PSL_TRACED)
358 p->p_pax &= ~P_PAX_MPROTECT;
359 #endif
360 }
361
362 void
pax_setup_elf_flags(struct exec_package * epp,uint32_t elf_flags)363 pax_setup_elf_flags(struct exec_package *epp, uint32_t elf_flags)
364 {
365 uint32_t flags = 0;
366
367 #ifdef PAX_ASLR
368 if (pax_aslr_elf_flags_active(elf_flags)) {
369 flags |= P_PAX_ASLR;
370 }
371 #endif
372 #ifdef PAX_MPROTECT
373 if (pax_mprotect_elf_flags_active(elf_flags)) {
374 flags |= P_PAX_MPROTECT;
375 }
376 #endif
377 #ifdef PAX_SEGVGUARD
378 if (pax_segvguard_elf_flags_active(elf_flags)) {
379 flags |= P_PAX_GUARD;
380 }
381 #endif
382
383 epp->ep_pax_flags = flags;
384 }
385
386 #if defined(PAX_MPROTECT) || defined(PAX_SEGVGUARD) || defined(PAX_ASLR)
387 static inline bool
pax_flags_active(uint32_t flags,uint32_t opt)388 pax_flags_active(uint32_t flags, uint32_t opt)
389 {
390 if (!(flags & opt))
391 return false;
392 return true;
393 }
394 #endif /* PAX_MPROTECT || PAX_SEGVGUARD || PAX_ASLR */
395
396 #ifdef PAX_MPROTECT
397 static bool
pax_mprotect_elf_flags_active(uint32_t flags)398 pax_mprotect_elf_flags_active(uint32_t flags)
399 {
400 if (!pax_mprotect_enabled)
401 return false;
402 if (pax_mprotect_global && (flags & ELF_NOTE_PAX_NOMPROTECT) != 0) {
403 /* Mprotect explicitly disabled */
404 return false;
405 }
406 if (!pax_mprotect_global && (flags & ELF_NOTE_PAX_MPROTECT) == 0) {
407 /* Mprotect not requested */
408 return false;
409 }
410 return true;
411 }
412
413 vm_prot_t
pax_mprotect_maxprotect(const char * file,size_t line,struct lwp * l,vm_prot_t active,vm_prot_t extra,vm_prot_t maxprot)414 pax_mprotect_maxprotect(
415 #ifdef PAX_MPROTECT_DEBUG
416 const char *file, size_t line,
417 #endif
418 struct lwp *l, vm_prot_t active, vm_prot_t extra, vm_prot_t maxprot)
419 {
420 uint32_t flags;
421
422 flags = l->l_proc->p_pax;
423 if (!pax_flags_active(flags, P_PAX_MPROTECT))
424 return maxprot;
425
426 return (active|extra) & maxprot;
427 }
428
429 int
pax_mprotect_validate(const char * file,size_t line,struct lwp * l,vm_prot_t prot)430 pax_mprotect_validate(
431 #ifdef PAX_MPROTECT_DEBUG
432 const char *file, size_t line,
433 #endif
434 struct lwp *l, vm_prot_t prot)
435 {
436 uint32_t flags;
437
438 flags = l->l_proc->p_pax;
439 if (!pax_flags_active(flags, P_PAX_MPROTECT))
440 return 0;
441
442 if ((prot & (VM_PROT_WRITE|VM_PROT_EXECUTE)) ==
443 (VM_PROT_WRITE|VM_PROT_EXECUTE)) {
444 #ifdef PAX_MPROTECT_DEBUG
445 struct proc *p = l->l_proc;
446
447 if (pax_mprotect_debug)
448 printf("%s: %s,%zu: %d.%d (%s): WX rejected\n",
449 __func__, file, line,
450 p->p_pid, l->l_lid, p->p_comm);
451 #endif
452 return EACCES;
453 }
454 return 0;
455 }
456
457 /*
458 * Bypass MPROTECT for traced processes
459 */
460 int
pax_mprotect_prot(struct lwp * l)461 pax_mprotect_prot(struct lwp *l)
462 {
463 uint32_t flags;
464
465 flags = l->l_proc->p_pax;
466 if (!pax_flags_active(flags, P_PAX_MPROTECT))
467 return 0;
468 if (pax_mprotect_ptrace < 2)
469 return 0;
470 return UVM_EXTRACT_PROT_ALL;
471 }
472
473
474 #endif /* PAX_MPROTECT */
475
476 #ifdef PAX_ASLR
477 static bool
pax_aslr_elf_flags_active(uint32_t flags)478 pax_aslr_elf_flags_active(uint32_t flags)
479 {
480 if (!pax_aslr_enabled)
481 return false;
482 if (pax_aslr_global && (flags & ELF_NOTE_PAX_NOASLR) != 0) {
483 /* ASLR explicitly disabled */
484 return false;
485 }
486 if (!pax_aslr_global && (flags & ELF_NOTE_PAX_ASLR) == 0) {
487 /* ASLR not requested */
488 return false;
489 }
490 return true;
491 }
492
493 static bool
pax_aslr_epp_active(struct exec_package * epp)494 pax_aslr_epp_active(struct exec_package *epp)
495 {
496 if (__predict_false((epp->ep_flags & (EXEC_32|EXEC_TOPDOWN_VM)) == 0))
497 return false;
498 return pax_flags_active(epp->ep_pax_flags, P_PAX_ASLR);
499 }
500
501 static bool
pax_aslr_active(struct lwp * l)502 pax_aslr_active(struct lwp *l)
503 {
504 return pax_flags_active(l->l_proc->p_pax, P_PAX_ASLR);
505 }
506
507 void
pax_aslr_init_vm(struct lwp * l,struct vmspace * vm,struct exec_package * ep)508 pax_aslr_init_vm(struct lwp *l, struct vmspace *vm, struct exec_package *ep)
509 {
510 if (!pax_aslr_active(l))
511 return;
512
513 if (__predict_false((ep->ep_flags & (EXEC_32|EXEC_TOPDOWN_VM)) == 0))
514 return;
515
516 #ifdef PAX_ASLR_DEBUG
517 if (pax_aslr_flags & PAX_ASLR_MMAP)
518 return;
519 #endif
520
521 uint32_t len = (ep->ep_flags & EXEC_32) ?
522 PAX_ASLR_DELTA_MMAP_LEN32 : PAX_ASLR_DELTA_MMAP_LEN;
523
524 uint32_t rand = cprng_fast32();
525 #ifdef PAX_ASLR_DEBUG
526 if (pax_aslr_flags & PAX_ASLR_FIXED)
527 rand = pax_aslr_rand;
528 #endif
529 vm->vm_aslr_delta_mmap = PAX_ASLR_DELTA(rand,
530 PAX_ASLR_DELTA_MMAP_LSB, len);
531
532 PAX_DPRINTF("delta_mmap=%#jx/%u",
533 (uintmax_t)vm->vm_aslr_delta_mmap, len);
534 }
535
536 void
pax_aslr_mmap(struct lwp * l,vaddr_t * addr,vaddr_t orig_addr,int f)537 pax_aslr_mmap(struct lwp *l, vaddr_t *addr, vaddr_t orig_addr, int f)
538 {
539 if (!pax_aslr_active(l))
540 return;
541 #ifdef PAX_ASLR_DEBUG
542 char buf[256];
543
544 if (pax_aslr_flags & PAX_ASLR_MMAP)
545 return;
546
547 if (pax_aslr_debug)
548 snprintb(buf, sizeof(buf), MAP_FMT, f);
549 else
550 buf[0] = '\0';
551 #endif
552
553 if (!(f & MAP_FIXED) && ((orig_addr == 0) || !(f & MAP_ANON))) {
554 PAX_DPRINTF("applying to %#jx orig_addr=%#jx f=%s",
555 (uintmax_t)*addr, (uintmax_t)orig_addr, buf);
556 if (!(l->l_proc->p_vmspace->vm_map.flags & VM_MAP_TOPDOWN))
557 *addr += l->l_proc->p_vmspace->vm_aslr_delta_mmap;
558 else
559 *addr -= l->l_proc->p_vmspace->vm_aslr_delta_mmap;
560 PAX_DPRINTF("result %#jx", (uintmax_t)*addr);
561 } else {
562 PAX_DPRINTF("not applying to %#jx orig_addr=%#jx f=%s",
563 (uintmax_t)*addr, (uintmax_t)orig_addr, buf);
564 }
565 }
566
567 static vaddr_t
pax_aslr_offset(vaddr_t align)568 pax_aslr_offset(vaddr_t align)
569 {
570 size_t pax_align, l2, delta;
571 uint32_t rand;
572 vaddr_t offset;
573
574 pax_align = align == 0 ? PAGE_SIZE : align;
575 l2 = ilog2(pax_align);
576
577 rand = cprng_fast32();
578 #ifdef PAX_ASLR_DEBUG
579 if (pax_aslr_flags & PAX_ASLR_FIXED)
580 rand = pax_aslr_rand;
581 #endif
582
583 #define PAX_TRUNC(a, b) ((a) & ~((b) - 1))
584
585 delta = PAX_ASLR_DELTA(rand, l2, PAX_ASLR_DELTA_EXEC_LEN);
586 offset = PAX_TRUNC(delta, pax_align);
587 offset = MAX(offset, pax_align);
588
589 PAX_DPRINTF("rand=%#x l2=%#zx pax_align=%#zx delta=%#zx offset=%#jx",
590 rand, l2, pax_align, delta, (uintmax_t)offset);
591
592 return offset;
593 }
594
595 vaddr_t
pax_aslr_exec_offset(struct exec_package * epp,vaddr_t align)596 pax_aslr_exec_offset(struct exec_package *epp, vaddr_t align)
597 {
598 if (!pax_aslr_epp_active(epp))
599 goto out;
600
601 #ifdef PAX_ASLR_DEBUG
602 if (pax_aslr_flags & PAX_ASLR_EXEC_OFFSET)
603 goto out;
604 #endif
605 return pax_aslr_offset(align);
606 out:
607 return MAX(align, PAGE_SIZE);
608 }
609
610 voff_t
pax_aslr_rtld_offset(struct exec_package * epp,vaddr_t align,int use_topdown)611 pax_aslr_rtld_offset(struct exec_package *epp, vaddr_t align, int use_topdown)
612 {
613 voff_t offset;
614
615 if (!pax_aslr_epp_active(epp))
616 return 0;
617
618 #ifdef PAX_ASLR_DEBUG
619 if (pax_aslr_flags & PAX_ASLR_RTLD_OFFSET)
620 return 0;
621 #endif
622 offset = pax_aslr_offset(align);
623 if (use_topdown)
624 offset = -offset;
625
626 return offset;
627 }
628
629 void
pax_aslr_stack(struct exec_package * epp,vsize_t * max_stack_size)630 pax_aslr_stack(struct exec_package *epp, vsize_t *max_stack_size)
631 {
632 if (!pax_aslr_epp_active(epp))
633 return;
634 #ifdef PAX_ASLR_DEBUG
635 if (pax_aslr_flags & PAX_ASLR_STACK)
636 return;
637 #endif
638
639 uint32_t len = (epp->ep_flags & EXEC_32) ?
640 PAX_ASLR_DELTA_STACK_LEN32 : PAX_ASLR_DELTA_STACK_LEN;
641 uint32_t rand = cprng_fast32();
642 #ifdef PAX_ASLR_DEBUG
643 if (pax_aslr_flags & PAX_ASLR_FIXED)
644 rand = pax_aslr_rand;
645 #endif
646 u_long d = PAX_ASLR_DELTA(rand, PAX_ASLR_DELTA_STACK_LSB, len);
647 d &= (*max_stack_size / PAX_ASLR_MAX_STACK_WASTE) - 1;
648 u_long newminsaddr = (u_long)STACK_GROW(epp->ep_minsaddr, d);
649 PAX_DPRINTF("old minsaddr=%#jx delta=%#lx new minsaddr=%#lx",
650 (uintmax_t)epp->ep_minsaddr, d, newminsaddr);
651 epp->ep_minsaddr = (vaddr_t)newminsaddr;
652 *max_stack_size -= d;
653 }
654
655 uint32_t
pax_aslr_stack_gap(struct exec_package * epp)656 pax_aslr_stack_gap(struct exec_package *epp)
657 {
658 if (!pax_aslr_epp_active(epp))
659 return 0;
660
661 #ifdef PAX_ASLR_DEBUG
662 if (pax_aslr_flags & PAX_ASLR_STACK_GAP)
663 return 0;
664 #endif
665
666 uint32_t rand = cprng_fast32();
667 #ifdef PAX_ASLR_DEBUG
668 if (pax_aslr_flags & PAX_ASLR_FIXED)
669 rand = pax_aslr_rand;
670 #endif
671 rand %= PAGE_SIZE;
672 PAX_DPRINTF("stack gap=%#x\n", rand);
673 return rand;
674 }
675 #endif /* PAX_ASLR */
676
677 #ifdef PAX_SEGVGUARD
678 static bool
pax_segvguard_elf_flags_active(uint32_t flags)679 pax_segvguard_elf_flags_active(uint32_t flags)
680 {
681 if (!pax_segvguard_enabled)
682 return false;
683 if (pax_segvguard_global && (flags & ELF_NOTE_PAX_NOGUARD) != 0) {
684 /* Segvguard explicitly disabled */
685 return false;
686 }
687 if (!pax_segvguard_global && (flags & ELF_NOTE_PAX_GUARD) == 0) {
688 /* Segvguard not requested */
689 return false;
690 }
691 return true;
692 }
693
694 void
pax_segvguard_cleanup(struct vnode * vp)695 pax_segvguard_cleanup(struct vnode *vp)
696 {
697 struct pax_segvguard_entry *p = vp->v_segvguard;
698 struct pax_segvguard_uid_entry *up;
699
700 if (__predict_true(p == NULL)) {
701 return;
702 }
703 while ((up = LIST_FIRST(&p->segv_uids)) != NULL) {
704 LIST_REMOVE(up, sue_list);
705 kmem_free(up, sizeof(*up));
706 }
707 kmem_free(p, sizeof(*p));
708 vp->v_segvguard = NULL;
709 }
710
711 /*
712 * Called when a process of image vp generated a segfault.
713 *
714 * => exec_lock must be held by the caller
715 * => if "crashed" is true, exec_lock must be held for write
716 */
717 int
pax_segvguard(struct lwp * l,struct vnode * vp,const char * name,bool crashed)718 pax_segvguard(struct lwp *l, struct vnode *vp, const char *name, bool crashed)
719 {
720 struct pax_segvguard_entry *p;
721 struct pax_segvguard_uid_entry *up;
722 struct timeval tv;
723 uid_t uid;
724 uint32_t flags;
725 bool have_uid;
726
727 KASSERT(rw_lock_held(&exec_lock));
728 KASSERT(!crashed || rw_write_held(&exec_lock));
729
730 flags = l->l_proc->p_pax;
731 if (!pax_flags_active(flags, P_PAX_GUARD))
732 return 0;
733
734 if (vp == NULL)
735 return EFAULT;
736
737 /* Fast-path if starting a program we don't know. */
738 if ((p = vp->v_segvguard) == NULL && !crashed)
739 return 0;
740
741 microtime(&tv);
742
743 /*
744 * If a program we don't know crashed, we need to create a new entry
745 * for it.
746 */
747 if (p == NULL) {
748 p = kmem_alloc(sizeof(*p), KM_SLEEP);
749 vp->v_segvguard = p;
750 LIST_INIT(&p->segv_uids);
751
752 /*
753 * Initialize a new entry with "crashes so far" of 1.
754 * The expiry time is when we purge the entry if it didn't
755 * reach the limit.
756 */
757 up = kmem_alloc(sizeof(*up), KM_SLEEP);
758 up->sue_uid = kauth_cred_getuid(l->l_cred);
759 up->sue_ncrashes = 1;
760 up->sue_expiry = tv.tv_sec + pax_segvguard_expiry;
761 up->sue_suspended = 0;
762 LIST_INSERT_HEAD(&p->segv_uids, up, sue_list);
763 return 0;
764 }
765
766 /*
767 * A program we "know" either executed or crashed again.
768 * See if it's a culprit we're familiar with.
769 */
770 uid = kauth_cred_getuid(l->l_cred);
771 have_uid = false;
772 LIST_FOREACH(up, &p->segv_uids, sue_list) {
773 if (up->sue_uid == uid) {
774 have_uid = true;
775 break;
776 }
777 }
778
779 /*
780 * It's someone else. Add an entry for him if we crashed.
781 */
782 if (!have_uid) {
783 if (crashed) {
784 up = kmem_alloc(sizeof(*up), KM_SLEEP);
785 up->sue_uid = uid;
786 up->sue_ncrashes = 1;
787 up->sue_expiry = tv.tv_sec + pax_segvguard_expiry;
788 up->sue_suspended = 0;
789 LIST_INSERT_HEAD(&p->segv_uids, up, sue_list);
790 }
791 return 0;
792 }
793
794 if (crashed) {
795 /* Check if timer on previous crashes expired first. */
796 if (up->sue_expiry < tv.tv_sec) {
797 log(LOG_INFO, "PaX Segvguard: [%s] Suspension"
798 " expired.\n", name ? name : "unknown");
799 up->sue_ncrashes = 1;
800 up->sue_expiry = tv.tv_sec + pax_segvguard_expiry;
801 up->sue_suspended = 0;
802 return 0;
803 }
804
805 up->sue_ncrashes++;
806
807 if (up->sue_ncrashes >= pax_segvguard_maxcrashes) {
808 log(LOG_ALERT, "PaX Segvguard: [%s] Suspending "
809 "execution for %d seconds after %zu crashes.\n",
810 name ? name : "unknown", pax_segvguard_suspension,
811 up->sue_ncrashes);
812
813 /* Suspend this program for a while. */
814 up->sue_suspended = tv.tv_sec + pax_segvguard_suspension;
815 up->sue_ncrashes = 0;
816 up->sue_expiry = 0;
817 }
818 } else {
819 /* Are we supposed to be suspended? */
820 if (up->sue_suspended > tv.tv_sec) {
821 log(LOG_ALERT, "PaX Segvguard: [%s] Preventing "
822 "execution due to repeated segfaults.\n", name ?
823 name : "unknown");
824 return EPERM;
825 }
826 }
827
828 return 0;
829 }
830 #endif /* PAX_SEGVGUARD */
831