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Allow sharing the RELRO section via a file.

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Add flags and a file descriptor to android_dlopen_ext() to allow writing
the RELRO section of the loaded library to a file after relocation
processing, and to allow mapping identical pages from the file over the
top of relocated memory in another process. Explicitly comparing the
pages is required in case a page contains a reference to a symbol
defined in another library loaded at a random base address.

Bug: 13005501
Change-Id: Ibb5b2d384edfaa5acf3e97a5f8b6115c10497a1e
This commit is contained in:
Torne (Richard Coles)
2014-02-27 13:18:00 +00:00
parent 12bbb91645
commit 183ad9df53
5 changed files with 226 additions and 6 deletions
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18
libc/include/android/dlext.h
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@@ -36,15 +36,31 @@ enum {
*/
ANDROID_DLEXT_RESERVED_ADDRESS_HINT = 0x2,
/* When set, write the GNU RELRO section of the mapped library to relro_fd
* after relocation has been performed, to allow it to be reused by another
* process loading the same library at the same address. This implies
* ANDROID_DLEXT_USE_RELRO.
*/
ANDROID_DLEXT_WRITE_RELRO = 0x4,
/* When set, compare the GNU RELRO section of the mapped library to relro_fd
* after relocation has been performed, and replace any relocated pages that
* are identical with a version mapped from the file.
*/
ANDROID_DLEXT_USE_RELRO = 0x8,
/* Mask of valid bits */
ANDROID_DLEXT_VALID_FLAG_BITS = ANDROID_DLEXT_RESERVED_ADDRESS |
ANDROID_DLEXT_RESERVED_ADDRESS_HINT,
ANDROID_DLEXT_RESERVED_ADDRESS_HINT |
ANDROID_DLEXT_WRITE_RELRO |
ANDROID_DLEXT_USE_RELRO,
};
typedef struct {
int flags;
void* reserved_addr;
size_t reserved_size;
int relro_fd;
} android_dlextinfo;
extern void* android_dlopen_ext(const char* filename, int flag, const android_dlextinfo* extinfo);