84 lines
3.3 KiB
C
84 lines
3.3 KiB
C
/* Allocate a stack suitable to be used with xclone or xsigaltstack.
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Copyright (C) 2021-2022 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/check.h>
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#include <support/support.h>
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#include <support/xunistd.h>
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#include <stdint.h>
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#include <string.h>
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#include <stackinfo.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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struct support_stack
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support_stack_alloc (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 sysconf (_SC_SIGSTKSZ) space; passing 0
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as size means only that much space. No matter what the number is,
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round it up to a whole number of pages. */
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size_t stacksize = roundup (size + sysconf (_SC_SIGSTKSZ),
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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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size_t 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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void *alloc_base = xmmap (0,
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alloc_size,
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PROT_NONE,
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MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE|MAP_STACK,
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-1);
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/* Some architecture still requires executable stack for the signal return
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trampoline, although PF_X could be overridden if PT_GNU_STACK is present.
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However since glibc does not export such information with a proper ABI,
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it uses the historical permissions. */
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int prot = PROT_READ | PROT_WRITE
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| (DEFAULT_STACK_PERMS & PF_X ? PROT_EXEC : 0);
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xmprotect (alloc_base + guardsize, stacksize, prot);
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memset (alloc_base + guardsize, 0xA5, stacksize);
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return (struct support_stack) { alloc_base + guardsize, stacksize, guardsize };
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}
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void
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support_stack_free (struct support_stack *stack)
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{
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void *alloc_base = (void *)((uintptr_t) stack->stack - stack->guardsize);
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size_t alloc_size = stack->size + 2 * stack->guardsize;
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xmunmap (alloc_base, alloc_size);
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}
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