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Diffstat (limited to 'support/xsigstack.c')
| -rw-r--r-- | support/xsigstack.c | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/support/xsigstack.c b/support/xsigstack.c new file mode 100644 index 0000000000..cebfa19aa5 --- /dev/null +++ b/support/xsigstack.c @@ -0,0 +1,107 @@ +/* sigaltstack wrappers. + Copyright (C) 2019 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <support/xsignal.h> +#include <support/support.h> +#include <support/xunistd.h> +#include <support/check.h> + +#include <stdlib.h> +#include <string.h> +#include <sys/mman.h> +#include <sys/param.h> /* roundup, MAX */ + +/* The "cookie" returned by xalloc_sigstack points to one of these + structures. */ +struct sigstack_desc +{ + void *alloc_base; /* Base address of the complete allocation. */ + size_t alloc_size; /* Size of the complete allocation. */ + stack_t alt_stack; /* The address and size of the stack itself. */ + stack_t old_stack; /* The previous signal stack. */ +}; + +void * +xalloc_sigstack (size_t size) +{ + size_t pagesize = sysconf (_SC_PAGESIZE); + if (pagesize == -1) + FAIL_EXIT1 ("sysconf (_SC_PAGESIZE): %m\n"); + + /* Always supply at least MINSIGSTKSZ space; passing 0 as size means + only that much space. No matter what the number is, round it up + to a whole number of pages. */ + size_t stacksize = roundup (size + MINSIGSTKSZ, pagesize); + + /* The guard bands need to be large enough to intercept offset + accesses from a stack address that might otherwise hit another + mapping. Make them at least twice as big as the stack itself, to + defend against an offset by the entire size of a large + stack-allocated array. The minimum is 1MiB, which is arbitrarily + chosen to be larger than any "typical" wild pointer offset. + Again, no matter what the number is, round it up to a whole + number of pages. */ + size_t guardsize = roundup (MAX (2 * stacksize, 1024 * 1024), pagesize); + + struct sigstack_desc *desc = xmalloc (sizeof (struct sigstack_desc)); + desc->alloc_size = guardsize + stacksize + guardsize; + /* Use MAP_NORESERVE so that RAM will not be wasted on the guard + bands; touch all the pages of the actual stack before returning, + so we know they are allocated. */ + desc->alloc_base = xmmap (0, + desc->alloc_size, + PROT_READ|PROT_WRITE, + MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE|MAP_STACK, + -1); + + xmprotect (desc->alloc_base, guardsize, PROT_NONE); + xmprotect (desc->alloc_base + guardsize + stacksize, guardsize, PROT_NONE); + memset (desc->alloc_base + guardsize, 0xA5, stacksize); + + desc->alt_stack.ss_sp = desc->alloc_base + guardsize; + desc->alt_stack.ss_flags = 0; + desc->alt_stack.ss_size = stacksize; + + if (sigaltstack (&desc->alt_stack, &desc->old_stack)) + FAIL_EXIT1 ("sigaltstack (new stack: sp=%p, size=%zu, flags=%u): %m\n", + desc->alt_stack.ss_sp, desc->alt_stack.ss_size, + desc->alt_stack.ss_flags); + + return desc; +} + +void +xfree_sigstack (void *stack) +{ + struct sigstack_desc *desc = stack; + + if (sigaltstack (&desc->old_stack, 0)) + FAIL_EXIT1 ("sigaltstack (restore old stack: sp=%p, size=%zu, flags=%u): " + "%m\n", desc->old_stack.ss_sp, desc->old_stack.ss_size, + desc->old_stack.ss_flags); + xmunmap (desc->alloc_base, desc->alloc_size); + free (desc); +} + +void +xget_sigstack_location (const void *stack, unsigned char **addrp, size_t *sizep) +{ + const struct sigstack_desc *desc = stack; + *addrp = desc->alt_stack.ss_sp; + *sizep = desc->alt_stack.ss_size; +} |