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LibC: Randomize the stack check cookie value on initialization
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.
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2 changed files with 26 additions and 0 deletions
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@ -33,6 +33,8 @@
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extern "C" {
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extern u32 __stack_chk_guard;
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int main(int, char**, char**);
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extern void __libc_init();
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@ -43,9 +45,20 @@ extern bool __environ_is_malloced;
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int _start(int argc, char** argv, char** env);
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int _start(int argc, char** argv, char** env)
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{
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u32 original_stack_chk = __stack_chk_guard;
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arc4random_buf(&__stack_chk_guard, sizeof(__stack_chk_guard));
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if (__stack_chk_guard == 0)
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__stack_chk_guard = original_stack_chk;
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_init();
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int status = main(argc, argv, env);
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// Restore the stack guard to the value we entered _start with,
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// so we don't trigger the stack canary check on the way out.
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__stack_chk_guard = original_stack_chk;
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return status;
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}
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}
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