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115 lines
4.1 KiB
C
115 lines
4.1 KiB
C
/* sigaltstack wrappers.
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Copyright (C) 2019-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <support/xsignal.h>
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#include <support/support.h>
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#include <support/xunistd.h>
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#include <support/check.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <sys/param.h> /* roundup, MAX */
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#ifndef MAP_NORESERVE
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# define MAP_NORESERVE 0
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#endif
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#ifndef MAP_STACK
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# define MAP_STACK 0
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#endif
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/* The "cookie" returned by xalloc_sigstack points to one of these
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structures. */
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struct sigstack_desc
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{
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void *alloc_base; /* Base address of the complete allocation. */
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size_t alloc_size; /* Size of the complete allocation. */
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stack_t alt_stack; /* The address and size of the stack itself. */
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stack_t old_stack; /* The previous signal stack. */
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};
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void *
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xalloc_sigstack (size_t size)
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{
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size_t pagesize = sysconf (_SC_PAGESIZE);
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if (pagesize == -1)
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FAIL_EXIT1 ("sysconf (_SC_PAGESIZE): %m\n");
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/* Always supply at least MINSIGSTKSZ space; passing 0 as size means
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only that much space. No matter what the number is, round it up
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to a whole number of pages. */
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size_t stacksize = roundup (size + MINSIGSTKSZ, pagesize);
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/* The guard bands need to be large enough to intercept offset
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accesses from a stack address that might otherwise hit another
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mapping. Make them at least twice as big as the stack itself, to
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defend against an offset by the entire size of a large
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stack-allocated array. The minimum is 1MiB, which is arbitrarily
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chosen to be larger than any "typical" wild pointer offset.
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Again, no matter what the number is, round it up to a whole
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number of pages. */
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size_t guardsize = roundup (MAX (2 * stacksize, 1024 * 1024), pagesize);
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struct sigstack_desc *desc = xmalloc (sizeof (struct sigstack_desc));
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desc->alloc_size = guardsize + stacksize + guardsize;
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/* Use MAP_NORESERVE so that RAM will not be wasted on the guard
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bands; touch all the pages of the actual stack before returning,
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so we know they are allocated. */
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desc->alloc_base = xmmap (0,
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desc->alloc_size,
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PROT_READ|PROT_WRITE,
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MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE|MAP_STACK,
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-1);
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xmprotect (desc->alloc_base, guardsize, PROT_NONE);
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xmprotect (desc->alloc_base + guardsize + stacksize, guardsize, PROT_NONE);
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memset (desc->alloc_base + guardsize, 0xA5, stacksize);
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desc->alt_stack.ss_sp = desc->alloc_base + guardsize;
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desc->alt_stack.ss_flags = 0;
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desc->alt_stack.ss_size = stacksize;
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if (sigaltstack (&desc->alt_stack, &desc->old_stack))
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FAIL_EXIT1 ("sigaltstack (new stack: sp=%p, size=%zu, flags=%u): %m\n",
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desc->alt_stack.ss_sp, desc->alt_stack.ss_size,
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desc->alt_stack.ss_flags);
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return desc;
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}
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void
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xfree_sigstack (void *stack)
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{
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struct sigstack_desc *desc = stack;
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if (sigaltstack (&desc->old_stack, 0))
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FAIL_EXIT1 ("sigaltstack (restore old stack: sp=%p, size=%zu, flags=%u): "
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"%m\n", desc->old_stack.ss_sp, desc->old_stack.ss_size,
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desc->old_stack.ss_flags);
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xmunmap (desc->alloc_base, desc->alloc_size);
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free (desc);
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}
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void
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xget_sigstack_location (const void *stack, unsigned char **addrp, size_t *sizep)
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{
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const struct sigstack_desc *desc = stack;
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*addrp = desc->alt_stack.ss_sp;
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*sizep = desc->alt_stack.ss_size;
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}
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