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

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.