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/* AArch64 GCS allocation.
Copyright (C) 2024-2025 Free Software Foundation, Inc.
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 <unistd.h>
#include <sys/mman.h>
#ifndef SHADOW_STACK_SET_TOKEN
# define SHADOW_STACK_SET_TOKEN (1UL << 0)
# define SHADOW_STACK_SET_MARKER (1UL << 1)
#endif
static void *
map_shadow_stack (void *addr, size_t size, unsigned long flags)
{
return (void *) INLINE_SYSCALL_CALL (map_shadow_stack, addr, size, flags);
}
#define GCS_MAX_SIZE (1UL << 31)
#define GCS_ALTSTACK_RESERVE 160
void *
__alloc_gcs (size_t stack_size, void **ss_base, size_t *ss_size)
{
size_t size = (stack_size / 2 + GCS_ALTSTACK_RESERVE) & -8UL;
if (size > GCS_MAX_SIZE)
size = GCS_MAX_SIZE;
unsigned long flags = SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN;
void *base = map_shadow_stack (NULL, size, flags);
if (base == MAP_FAILED)
return NULL;
*ss_base = base;
*ss_size = size;
uint64_t *gcsp = (uint64_t *) ((char *) base + size);
/* Skip end of GCS token. */
gcsp--;
/* Verify GCS cap token. */
gcsp--;
if (((uint64_t)gcsp & 0xfffffffffffff000) + 1 != *gcsp)
{
__munmap (base, size);
return NULL;
}
/* Return the target GCS pointer for context switch. */
return gcsp + 1;
}
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