Re: [PATCH v28 26/32] x86/cet/shstk: Introduce shadow stack token setup/verify routines

Dave Hansen
2021-07-22T21:15:39Z

On 7/22/21 1:52 PM, Yu-cheng Yu wrote:
> + if (fpregs_state_valid(fpu, smp_processor_id())) {
> + rdmsrl(MSR_IA32_PL3_SSP, ssp);
> + } else {
> + struct cet_user_state *p;
> +
> + /*
> + * When !fpregs_state_valid() and get_xsave_addr() returns
> + * null, XFEAUTRE_CET_USER is in init state. Shadow stack
> + * pointer is null in this case, so return zero.
> + */
> + p = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER);
> + if (p)
> + ssp = p->user_ssp;
> + }
> +
> + fpregs_unlock();

Why are we even calling into this code if shadow stacks might be
disabled? Seems like we should have just errored out long before
getting here.