diff options
Diffstat (limited to 'support')
| -rw-r--r-- | support/Makefile | 1 | ||||
| -rw-r--r-- | support/next_to_fault.c | 52 | ||||
| -rw-r--r-- | support/next_to_fault.h | 48 |
3 files changed, 101 insertions, 0 deletions
diff --git a/support/Makefile b/support/Makefile index dafb1737a4..f7a878b950 100644 --- a/support/Makefile +++ b/support/Makefile @@ -32,6 +32,7 @@ libsupport-routines = \ check_netent \ delayed_exit \ ignore_stderr \ + next_to_fault \ oom_error \ resolv_test \ set_fortify_handler \ diff --git a/support/next_to_fault.c b/support/next_to_fault.c new file mode 100644 index 0000000000..7c6b077898 --- /dev/null +++ b/support/next_to_fault.c @@ -0,0 +1,52 @@ +/* Memory allocation next to an unmapped page. + Copyright (C) 2017 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 <support/check.h> +#include <support/next_to_fault.h> +#include <support/xunistd.h> +#include <sys/mman.h> +#include <sys/param.h> + +struct support_next_to_fault +support_next_to_fault_allocate (size_t size) +{ + long page_size = sysconf (_SC_PAGE_SIZE); + TEST_VERIFY_EXIT (page_size > 0); + struct support_next_to_fault result; + result.region_size = roundup (size, page_size) + page_size; + if (size + page_size <= size || result.region_size <= size) + FAIL_EXIT1 ("support_next_to_fault_allocate (%zu): overflow", size); + result.region_start + = xmmap (NULL, result.region_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1); + /* Unmap the page after the allocation. */ + xmprotect (result.region_start + (result.region_size - page_size), + page_size, PROT_NONE); + /* Align the allocation within the region so that it ends just + before the PROT_NONE page. */ + result.buffer = result.region_start + result.region_size - page_size - size; + result.length = size; + return result; +} + +void +support_next_to_fault_free (struct support_next_to_fault *ntf) +{ + xmunmap (ntf->region_start, ntf->region_size); + *ntf = (struct support_next_to_fault) { NULL, }; +} diff --git a/support/next_to_fault.h b/support/next_to_fault.h new file mode 100644 index 0000000000..dd71c28ac0 --- /dev/null +++ b/support/next_to_fault.h @@ -0,0 +1,48 @@ +/* Memory allocation next to an unmapped page. + Copyright (C) 2017 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/>. */ + +#ifndef SUPPORT_NEXT_TO_FAULT_H +#define SUPPORT_NEXT_TO_FAULT_H + +#include <sys/cdefs.h> +#include <sys/types.h> + +__BEGIN_DECLS + +/* The memory region created by next_to_fault_allocate. */ +struct support_next_to_fault +{ + /* The user data. */ + char *buffer; + size_t length; + + /* The entire allocated region. */ + void *region_start; + size_t region_size; +}; + +/* Allocate a buffer of SIZE bytes just before a page which is mapped + with PROT_NONE (so that overrunning the buffer will cause a + fault). */ +struct support_next_to_fault support_next_to_fault_allocate (size_t size); + +/* Deallocate the memory region allocated by + next_to_fault_allocate. */ +void support_next_to_fault_free (struct support_next_to_fault *); + +#endif /* SUPPORT_NEXT_TO_FAULT_H */ |