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/* Helper function to allocate shadow stack.
Copyright (C) 2023-2025 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
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include <stdint.h>
#include <errno.h>
#include <sys/mman.h>
#include <libc-pointer-arith.h>
#include <allocate-shadow-stack.h>
/* NB: This can be treated as a syscall by caller. */
long int
__allocate_shadow_stack (size_t stack_size,
shadow_stack_size_t *child_stack)
{
#ifdef __NR_map_shadow_stack
size_t shadow_stack_size
= stack_size >> STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT;
/* Align shadow stack to 8 bytes. */
shadow_stack_size = ALIGN_UP (shadow_stack_size, 8);
/* Since sigaltstack shares shadow stack with the current context in
the thread, add extra 20 stack frames in shadow stack for signal
handlers. */
shadow_stack_size += 20 * 8;
void *shadow_stack = (void *)INLINE_SYSCALL_CALL
(map_shadow_stack, NULL, shadow_stack_size, SHADOW_STACK_SET_TOKEN);
/* Report the map_shadow_stack error. */
if (shadow_stack == MAP_FAILED)
return -errno;
/* Save the shadow stack base and size on child stack. */
child_stack[0] = (uintptr_t) shadow_stack;
child_stack[1] = shadow_stack_size;
return 0;
#else
return -ENOSYS;
#endif
}
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