diff options
| -rw-r--r-- | ChangeLog | 10 | ||||
| -rw-r--r-- | malloc/arena.c | 9 | ||||
| -rw-r--r-- | sysdeps/generic/malloc-sysdep.h | 25 | ||||
| -rw-r--r-- | sysdeps/unix/sysv/linux/malloc-sysdep.h | 57 |
4 files changed, 98 insertions, 3 deletions
@@ -1,5 +1,15 @@ 2012-09-25 Siddhesh Poyarekar <siddhesh@redhat.com> + * malloc/arena.c: Include malloc-sysdep.h. + (shrink_heap): Use check_may_shrink_heap to decide if madvise + is sufficient to shrink the heap or an unmap is needed. + * sysdeps/generic/malloc-sysdep.h: New file. Define + new function check_may_shrink_heap. + * sysdeps/unix/sysv/linux/malloc-sysdep.h: New file. Define + new function check_may_shrink_heap. + +2012-09-25 Siddhesh Poyarekar <siddhesh@redhat.com> + * libio/fileops.c (_IO_new_file_seekoff): Fix typos in comments. diff --git a/malloc/arena.c b/malloc/arena.c index f24e76c4f6..b209e3b7cd 100644 --- a/malloc/arena.c +++ b/malloc/arena.c @@ -19,6 +19,9 @@ #include <stdbool.h> +/* Get the implementation for check_may_shrink_heap. */ +#include <malloc-sysdep.h> + /* Compile-time constants. */ #define HEAP_MIN_SIZE (32*1024) @@ -621,9 +624,9 @@ shrink_heap(heap_info *h, long diff) new_size = (long)h->size - diff; if(new_size < (long)sizeof(*h)) return -1; - /* Try to re-map the extra heap space freshly to save memory, and - make it inaccessible. */ - if (__builtin_expect (__libc_enable_secure, 0)) + /* Try to re-map the extra heap space freshly to save memory, and make it + inaccessible. See malloc-sysdep.h to know when this is true. */ + if (__builtin_expect (check_may_shrink_heap (), 0)) { if((char *)MMAP((char *)h + new_size, diff, PROT_NONE, MAP_FIXED) == (char *) MAP_FAILED) diff --git a/sysdeps/generic/malloc-sysdep.h b/sysdeps/generic/malloc-sysdep.h new file mode 100644 index 0000000000..bbc48c04f0 --- /dev/null +++ b/sysdeps/generic/malloc-sysdep.h @@ -0,0 +1,25 @@ +/* System-specific malloc support functions. Generic version. + Copyright (C) 2012 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 + <http://www.gnu.org/licenses/>. */ + +/* Force an unmap when the heap shrinks in a secure exec. This ensures that + the old data pages immediately cease to be accessible. */ +static inline bool +check_may_shrink_heap (void) +{ + return __libc_enable_secure; +} diff --git a/sysdeps/unix/sysv/linux/malloc-sysdep.h b/sysdeps/unix/sysv/linux/malloc-sysdep.h new file mode 100644 index 0000000000..f926aeafff --- /dev/null +++ b/sysdeps/unix/sysv/linux/malloc-sysdep.h @@ -0,0 +1,57 @@ +/* System-specific malloc support functions. Linux version. + Copyright (C) 2012 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 + <http://www.gnu.org/licenses/>. */ + +#include <fcntl.h> +#include <not-cancel.h> + +/* The Linux kernel overcommits address space by default and if there is not + enough memory available, it uses various parameters to decide the process to + kill. It is however possible to disable or curb this overcommit behavior + by setting the proc sysctl vm.overcommit_memory to the value '2' and with + that, a process is only allowed to use the maximum of a pre-determined + fraction of the total address space. In such a case, we want to make sure + that we are judicious with our heap usage as well, and explicitly give away + the freed top of the heap to reduce our commit charge. See the proc(5) man + page to know more about overcommit behavior. + + Other than that, we also force an unmap in a secure exec. */ +static inline bool +check_may_shrink_heap (void) +{ + static int may_shrink_heap = -1; + + if (__builtin_expect (may_shrink_heap >= 0, 1)) + return may_shrink_heap; + + may_shrink_heap = __libc_enable_secure; + + if (__builtin_expect (may_shrink_heap == 0, 1)) + { + int fd = open_not_cancel_2 ("/proc/sys/vm/overcommit_memory", + O_RDONLY | O_CLOEXEC); + if (fd >= 0) + { + char val; + ssize_t n = read_not_cancel (fd, &val, 1); + may_shrink_heap = n > 0 && val == '2'; + close_not_cancel_no_status (fd); + } + } + + return may_shrink_heap; +} |