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60 lines
2.2 KiB
C
60 lines
2.2 KiB
C
/* System-specific malloc support functions. Linux version.
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Copyright (C) 2012-2017 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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<http://www.gnu.org/licenses/>. */
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#include <fcntl.h>
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#include <not-cancel.h>
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/* The Linux kernel overcommits address space by default and if there is not
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enough memory available, it uses various parameters to decide the process to
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kill. It is however possible to disable or curb this overcommit behavior
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by setting the proc sysctl vm.overcommit_memory to the value '2' and with
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that, a process is only allowed to use the maximum of a pre-determined
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fraction of the total address space. In such a case, we want to make sure
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that we are judicious with our heap usage as well, and explicitly give away
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the freed top of the heap to reduce our commit charge. See the proc(5) man
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page to know more about overcommit behavior.
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Other than that, we also force an unmap in a secure exec. */
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static inline bool
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check_may_shrink_heap (void)
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{
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static int may_shrink_heap = -1;
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if (__builtin_expect (may_shrink_heap >= 0, 1))
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return may_shrink_heap;
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may_shrink_heap = __libc_enable_secure;
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if (__builtin_expect (may_shrink_heap == 0, 1))
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{
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int fd = open_not_cancel_2 ("/proc/sys/vm/overcommit_memory",
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O_RDONLY | O_CLOEXEC);
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if (fd >= 0)
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{
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char val;
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ssize_t n = read_not_cancel (fd, &val, 1);
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may_shrink_heap = n > 0 && val == '2';
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close_not_cancel_no_status (fd);
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}
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}
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return may_shrink_heap;
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}
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#define HAVE_MREMAP 1
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