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Add support for the stackleak feature. It initializes the stack with the
poison value before returning from system calls which improves the kernel
security.
At the same time, disables the plugin in EFI stub code because EFI stub
is out of scope for the protection.
Tested on Loongson-3A5000 (enable GCC_PLUGIN_STACKLEAK and LKDTM):
# echo STACKLEAK_ERASING > /sys/kernel/debug/provoke-crash/DIRECT
# dmesg
lkdtm: Performing direct entry STACKLEAK_ERASING
lkdtm: stackleak stack usage:
high offset: 320 bytes
current: 448 bytes
lowest: 1264 bytes
tracked: 1264 bytes
untracked: 208 bytes
poisoned: 14528 bytes
low offset: 64 bytes
lkdtm: OK: the rest of the thread stack is properly erased
Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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