x86/fpu/xstate: Fix PKRU covert channel

When XCR0[9] is set, PKRU can be read and written from userspace with
XSAVE and XRSTOR, even when CR4.PKE is clear.

Clear XCR0[9] when protection keys are disabled.

Reported-by: Tavis Ormandy <taviso@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20230831043228.1194256-1-jmattson@google.com

Author: jsmattsonjr

arch/x86/kernel/fpu/xstate.c

@@ -71,7 +71,7 @@ static unsigned short xsave_cpuid_features[] __initdata = {
 	[XFEATURE_ZMM_Hi256]			= X86_FEATURE_AVX512F,
 	[XFEATURE_Hi16_ZMM]			= X86_FEATURE_AVX512F,
 	[XFEATURE_PT_UNIMPLEMENTED_SO_FAR]	= X86_FEATURE_INTEL_PT,
-	[XFEATURE_PKRU]				= X86_FEATURE_PKU,
+	[XFEATURE_PKRU]				= X86_FEATURE_OSPKE,
 	[XFEATURE_PASID]			= X86_FEATURE_ENQCMD,
 	[XFEATURE_XTILE_CFG]			= X86_FEATURE_AMX_TILE,
 	[XFEATURE_XTILE_DATA]			= X86_FEATURE_AMX_TILE,