| 1 | /* System-specific malloc support functions. Linux version. |
|---|
| 2 | Copyright (C) 2012-2024 Free Software Foundation, Inc. |
|---|
| 3 | This file is part of the GNU C Library. |
|---|
| 4 | |
|---|
| 5 | The GNU C Library is free software; you can redistribute it and/or |
|---|
| 6 | modify it under the terms of the GNU Lesser General Public |
|---|
| 7 | License as published by the Free Software Foundation; either |
|---|
| 8 | version 2.1 of the License, or (at your option) any later version. |
|---|
| 9 | |
|---|
| 10 | The GNU C Library is distributed in the hope that it will be useful, |
|---|
| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
|---|
| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
|---|
| 13 | Lesser General Public License for more details. |
|---|
| 14 | |
|---|
| 15 | You should have received a copy of the GNU Lesser General Public |
|---|
| 16 | License along with the GNU C Library; if not, see |
|---|
| 17 | <https://www.gnu.org/licenses/>. */ |
|---|
| 18 | |
|---|
| 19 | #include <fcntl.h> |
|---|
| 20 | #include <not-cancel.h> |
|---|
| 21 | |
|---|
| 22 | /* The Linux kernel overcommits address space by default and if there is not |
|---|
| 23 | enough memory available, it uses various parameters to decide the process to |
|---|
| 24 | kill. It is however possible to disable or curb this overcommit behavior |
|---|
| 25 | by setting the proc sysctl vm.overcommit_memory to the value '2' and with |
|---|
| 26 | that, a process is only allowed to use the maximum of a pre-determined |
|---|
| 27 | fraction of the total address space. In such a case, we want to make sure |
|---|
| 28 | that we are judicious with our heap usage as well, and explicitly give away |
|---|
| 29 | the freed top of the heap to reduce our commit charge. See the proc(5) man |
|---|
| 30 | page to know more about overcommit behavior. |
|---|
| 31 | |
|---|
| 32 | Other than that, we also force an unmap in a secure exec. */ |
|---|
| 33 | static inline bool |
|---|
| 34 | check_may_shrink_heap (void) |
|---|
| 35 | { |
|---|
| 36 | static int may_shrink_heap = -1; |
|---|
| 37 | |
|---|
| 38 | if (__builtin_expect (may_shrink_heap >= 0, 1)) |
|---|
| 39 | return may_shrink_heap; |
|---|
| 40 | |
|---|
| 41 | may_shrink_heap = __libc_enable_secure; |
|---|
| 42 | |
|---|
| 43 | if (__builtin_expect (may_shrink_heap == 0, 1)) |
|---|
| 44 | { |
|---|
| 45 | int fd = __open_nocancel ("/proc/sys/vm/overcommit_memory" , |
|---|
| 46 | O_RDONLY | O_CLOEXEC); |
|---|
| 47 | if (fd >= 0) |
|---|
| 48 | { |
|---|
| 49 | char val; |
|---|
| 50 | ssize_t n = __read_nocancel (fd, &val, 1); |
|---|
| 51 | may_shrink_heap = n > 0 && val == '2'; |
|---|
| 52 | __close_nocancel_nostatus (fd); |
|---|
| 53 | } |
|---|
| 54 | } |
|---|
| 55 | |
|---|
| 56 | return may_shrink_heap; |
|---|
| 57 | } |
|---|
| 58 | |
|---|
| 59 | #define HAVE_MREMAP 1 |
|---|
| 60 | |
|---|
