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LibC: Randomize the stack check cookie value on initialization

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Previously we had a static stack check cookie value for LibC.
Now we randomize the cookie value on LibC initialization, this should
help make the stack check more difficult to attack (still possible just
a bigger pain). This should also help to catch more bugs.
This commit is contained in:
Brian Gianforcaro 2021-01-02 04:27:35 -08:00 • committed by Andreas Kling
parent 9ec9d20e84
commit fd08c93ef5
2 changed files with 26 additions and 0 deletions
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13
Libraries/LibC/crt0_shared.cpp
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@ -33,6 +33,8 @@
extern "C" {
extern u32 __stack_chk_guard;
int main(int, char**, char**);
extern void __libc_init();
@ -43,9 +45,20 @@ extern bool __environ_is_malloced;
int _start(int argc, char** argv, char** env);
int _start(int argc, char** argv, char** env)
{
u32 original_stack_chk = __stack_chk_guard;
arc4random_buf(&__stack_chk_guard, sizeof(__stack_chk_guard));
if (__stack_chk_guard == 0)
__stack_chk_guard = original_stack_chk;
_init();
int status = main(argc, argv, env);
// Restore the stack guard to the value we entered _start with,
// so we don't trigger the stack canary check on the way out.
__stack_chk_guard = original_stack_chk;
return status;
}
}