On 11/30/20 3:16 PM, Yu, Yu-cheng wrote: >> >> Do we have any other spots in the kernel where we care about: >> >> boot_cpu_has(X86_FEATURE_SHSTK) || >> boot_cpu_has(X86_FEATURE_IBT) >> >> ? If so, we could also address this by declaring a software-defined >> X86_FEATURE_CET and then setting it if SHSTK||IBT is supported, then we >> just put that one feature in xsave_cpuid_features[]. >> > > These features have different CPUIDs but are complementary parts. I > don't know if someday there will be shadow-stack-only CPUs, but an > IBT-only CPU is weird. What if the kernel checks that the CPU has both > features and presents only one feature flag (X86_FEATURE_CET), no > X86_FEATURE_SHSTK or X86_FEATURE_IBT? Logically, that's probably fine. But, X86_FEATURE_IBT/SHSTK are in a non-scattered leaf, so we'll kinda define them whether we like it or not. We'd have to go out of our way to *not* define them.
