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fbbc9a4e | 1 | /* sigaltstack wrappers. |
d614a753 | 2 | Copyright (C) 2019-2020 Free Software Foundation, Inc. |
fbbc9a4e ZW |
3 | This file is part of the GNU C Library. |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Lesser General Public | |
7 | License as published by the Free Software Foundation; either | |
8 | version 2.1 of the License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Lesser General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Lesser General Public | |
16 | License along with the GNU C Library; if not, see | |
5a82c748 | 17 | <https://www.gnu.org/licenses/>. */ |
fbbc9a4e ZW |
18 | |
19 | #include <support/xsignal.h> | |
20 | #include <support/support.h> | |
21 | #include <support/xunistd.h> | |
22 | #include <support/check.h> | |
23 | ||
24 | #include <stdlib.h> | |
25 | #include <string.h> | |
26 | #include <sys/mman.h> | |
27 | #include <sys/param.h> /* roundup, MAX */ | |
28 | ||
3367acdb AZ |
29 | #ifndef MAP_NORESERVE |
30 | # define MAP_NORESERVE 0 | |
31 | #endif | |
32 | #ifndef MAP_STACK | |
33 | # define MAP_STACK 0 | |
34 | #endif | |
35 | ||
fbbc9a4e ZW |
36 | /* The "cookie" returned by xalloc_sigstack points to one of these |
37 | structures. */ | |
38 | struct sigstack_desc | |
39 | { | |
40 | void *alloc_base; /* Base address of the complete allocation. */ | |
41 | size_t alloc_size; /* Size of the complete allocation. */ | |
42 | stack_t alt_stack; /* The address and size of the stack itself. */ | |
43 | stack_t old_stack; /* The previous signal stack. */ | |
44 | }; | |
45 | ||
46 | void * | |
47 | xalloc_sigstack (size_t size) | |
48 | { | |
49 | size_t pagesize = sysconf (_SC_PAGESIZE); | |
50 | if (pagesize == -1) | |
51 | FAIL_EXIT1 ("sysconf (_SC_PAGESIZE): %m\n"); | |
52 | ||
53 | /* Always supply at least MINSIGSTKSZ space; passing 0 as size means | |
54 | only that much space. No matter what the number is, round it up | |
55 | to a whole number of pages. */ | |
56 | size_t stacksize = roundup (size + MINSIGSTKSZ, pagesize); | |
57 | ||
58 | /* The guard bands need to be large enough to intercept offset | |
59 | accesses from a stack address that might otherwise hit another | |
60 | mapping. Make them at least twice as big as the stack itself, to | |
61 | defend against an offset by the entire size of a large | |
62 | stack-allocated array. The minimum is 1MiB, which is arbitrarily | |
63 | chosen to be larger than any "typical" wild pointer offset. | |
64 | Again, no matter what the number is, round it up to a whole | |
65 | number of pages. */ | |
66 | size_t guardsize = roundup (MAX (2 * stacksize, 1024 * 1024), pagesize); | |
67 | ||
68 | struct sigstack_desc *desc = xmalloc (sizeof (struct sigstack_desc)); | |
69 | desc->alloc_size = guardsize + stacksize + guardsize; | |
70 | /* Use MAP_NORESERVE so that RAM will not be wasted on the guard | |
71 | bands; touch all the pages of the actual stack before returning, | |
72 | so we know they are allocated. */ | |
73 | desc->alloc_base = xmmap (0, | |
74 | desc->alloc_size, | |
75 | PROT_READ|PROT_WRITE, | |
76 | MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE|MAP_STACK, | |
77 | -1); | |
78 | ||
79 | xmprotect (desc->alloc_base, guardsize, PROT_NONE); | |
80 | xmprotect (desc->alloc_base + guardsize + stacksize, guardsize, PROT_NONE); | |
81 | memset (desc->alloc_base + guardsize, 0xA5, stacksize); | |
82 | ||
83 | desc->alt_stack.ss_sp = desc->alloc_base + guardsize; | |
84 | desc->alt_stack.ss_flags = 0; | |
85 | desc->alt_stack.ss_size = stacksize; | |
86 | ||
87 | if (sigaltstack (&desc->alt_stack, &desc->old_stack)) | |
88 | FAIL_EXIT1 ("sigaltstack (new stack: sp=%p, size=%zu, flags=%u): %m\n", | |
89 | desc->alt_stack.ss_sp, desc->alt_stack.ss_size, | |
90 | desc->alt_stack.ss_flags); | |
91 | ||
92 | return desc; | |
93 | } | |
94 | ||
95 | void | |
96 | xfree_sigstack (void *stack) | |
97 | { | |
98 | struct sigstack_desc *desc = stack; | |
99 | ||
100 | if (sigaltstack (&desc->old_stack, 0)) | |
101 | FAIL_EXIT1 ("sigaltstack (restore old stack: sp=%p, size=%zu, flags=%u): " | |
102 | "%m\n", desc->old_stack.ss_sp, desc->old_stack.ss_size, | |
103 | desc->old_stack.ss_flags); | |
104 | xmunmap (desc->alloc_base, desc->alloc_size); | |
105 | free (desc); | |
106 | } | |
107 | ||
108 | void | |
109 | xget_sigstack_location (const void *stack, unsigned char **addrp, size_t *sizep) | |
110 | { | |
111 | const struct sigstack_desc *desc = stack; | |
112 | *addrp = desc->alt_stack.ss_sp; | |
113 | *sizep = desc->alt_stack.ss_size; | |
114 | } |