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stack protector: use AT_RANDOM

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Populate the stack canaries from the kernel supplied
AT_RANDOM value, which doesn't involve any system calls.
This is slightly faster (6 fewer syscalls) and avoids
unnecessarily reading /dev/urandom, which depletes entropy.

Bug: 7959813

Change-Id: If2b43100a2a9929666df3de56b6139fed969e0f1
This commit is contained in:
Nick Kralevich
2013-01-14 14:46:26 -08:00
parent 14e1975e13
commit e3a49a8661
6 changed files with 35 additions and 50 deletions
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8
linker/linker.cpp
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@@ -1785,7 +1785,7 @@ static bool soinfo_link_image(soinfo* si) {
* fixed it's own GOT. It is safe to make references to externs
* and other non-local data at this point.
*/
static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linker_base)
static unsigned __linker_init_post_relocation(uintptr_t* elfdata, unsigned linker_base)
{
static soinfo linker_soinfo;
@@ -1976,7 +1976,7 @@ static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linke
* Find the value of AT_BASE passed to us by the kernel. This is the load
* location of the linker.
*/
static unsigned find_linker_base(unsigned **elfdata) {
static unsigned find_linker_base(uintptr_t* elfdata) {
int argc = (int) *elfdata;
char **argv = (char**) (elfdata + 1);
unsigned *vecs = (unsigned*) (argv + argc + 1);
@@ -2032,8 +2032,8 @@ get_elf_exec_load_bias(const Elf32_Ehdr* elf)
* relocations, any attempt to reference an extern variable, extern
* function, or other GOT reference will generate a segfault.
*/
extern "C" unsigned __linker_init(unsigned **elfdata) {
unsigned linker_addr = find_linker_base(elfdata);
extern "C" unsigned __linker_init(uintptr_t* elfdata) {
uintptr_t linker_addr = find_linker_base(elfdata);
Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_addr;
Elf32_Phdr *phdr =
(Elf32_Phdr *)((unsigned char *) linker_addr + elf_hdr->e_phoff);