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SubjectRe: [PATCH v2 2/2] powerpc/32: add stack protector support
On Wed, Sep 19, 2018 at 11:14:45AM +0000, Christophe Leroy wrote:
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -112,6 +112,10 @@ KBUILD_LDFLAGS += -m elf$(BITS)$(LDEMULATION)
> KBUILD_ARFLAGS += --target=elf$(BITS)-$(GNUTARGET)
> endif
>
> +cflags-$(CONFIG_STACKPROTECTOR) += -mstack-protector-guard=tls
> +cflags-$(CONFIG_STACKPROTECTOR) += -mstack-protector-guard-reg=r2
> +cflags-$(CONFIG_STACKPROTECTOR) += -mstack-protector-guard-offset=4

This last line is only correct if !CONFIG_THREAD_INFO_IN_TASK; is that
always true? Add an assert somewhere maybe?

> + /*
> + * The stack_canary must be located at the offset given to
> + * -mstack-protector-guard-offset in the Makefile
> + */
> + BUILD_BUG_ON(offsetof(struct task_struct, stack_canary) != sizeof(long));

Well this will help :-)

It looks like it will be easy to enable on 64 bit as well.

> + /* Try to get a semi random initial value. */
> + get_random_bytes(&canary, sizeof(canary));
> + canary ^= mftb();
> + canary ^= LINUX_VERSION_CODE;

These last two lines are useless (or worse, they may give people the idea
that they are not!)
You should use wait_for_random_bytes I think.


Segher

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