| 1 | /* Helper function to allocate shadow stack. |
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| 2 | Copyright (C) 2023-2024 Free Software Foundation, Inc. |
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| 3 | This file is part of the GNU C Library. |
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| 4 | |
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| 5 | The GNU C Library is free software; you can redistribute it and/or |
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| 6 | modify it under the terms of the GNU Lesser General Public |
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| 7 | License as published by the Free Software Foundation; either |
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| 8 | version 2.1 of the License, or (at your option) any later version. |
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| 9 | |
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| 10 | The GNU C Library is distributed in the hope that it will be useful, |
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 13 | Lesser General Public License for more details. |
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| 14 | |
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| 15 | You should have received a copy of the GNU Lesser General Public |
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| 16 | License along with the GNU C Library; if not, see |
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| 17 | <https://www.gnu.org/licenses/>. */ |
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| 18 | |
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| 19 | #include <sysdep.h> |
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| 20 | #include <stdint.h> |
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| 21 | #include <errno.h> |
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| 22 | #include <sys/mman.h> |
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| 23 | #include <libc-pointer-arith.h> |
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| 24 | #include <allocate-shadow-stack.h> |
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| 25 | |
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| 26 | /* NB: This can be treated as a syscall by caller. */ |
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| 27 | |
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| 28 | long int |
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| 29 | __allocate_shadow_stack (size_t stack_size, |
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| 30 | shadow_stack_size_t *child_stack) |
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| 31 | { |
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| 32 | #ifdef __NR_map_shadow_stack |
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| 33 | size_t shadow_stack_size |
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| 34 | = stack_size >> STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT; |
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| 35 | /* Align shadow stack to 8 bytes. */ |
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| 36 | shadow_stack_size = ALIGN_UP (shadow_stack_size, 8); |
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| 37 | /* Since sigaltstack shares shadow stack with the current context in |
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| 38 | the thread, add extra 20 stack frames in shadow stack for signal |
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| 39 | handlers. */ |
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| 40 | shadow_stack_size += 20 * 8; |
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| 41 | void *shadow_stack = (void *)INLINE_SYSCALL_CALL |
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| 42 | (map_shadow_stack, NULL, shadow_stack_size, SHADOW_STACK_SET_TOKEN); |
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| 43 | /* Report the map_shadow_stack error. */ |
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| 44 | if (shadow_stack == MAP_FAILED) |
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| 45 | return -errno; |
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| 46 | |
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| 47 | /* Save the shadow stack base and size on child stack. */ |
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| 48 | child_stack[0] = (uintptr_t) shadow_stack; |
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| 49 | child_stack[1] = shadow_stack_size; |
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| 50 | |
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| 51 | return 0; |
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| 52 | #else |
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| 53 | return -ENOSYS; |
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| 54 | #endif |
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| 55 | } |
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| 56 | |
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