KVM: x86: Fix xsave cpuid exposing bug

From 00c920c96127d20d4c3bb790082700ae375c39a0 Mon Sep 17 00:00:00 2001
From: Liu Jinsong <[e-mail]>
Date: Fri, 21 Feb 2014 23:47:18 +0800
Subject: [PATCH] KVM: x86: Fix xsave cpuid exposing bug

EBX of cpuid(0xD, 0) is dynamic per XCR0 features enable/disable.
Bit 63 of XCR0 is reserved for future expansion.

Signed-off-by: Liu Jinsong <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/include/asm/xsave.h

···
 #define XSTATE_BNDCSR	0x10
 
 #define XSTATE_FPSSE	(XSTATE_FP | XSTATE_SSE)
+/* Bit 63 of XCR0 is reserved for future expansion */
+#define XSTATE_EXTEND_MASK	(~(XSTATE_FPSSE | (1ULL << 63)))
 
 #define FXSAVE_SIZE	512
 

arch/x86/kvm/cpuid.c

···
 	int feature_bit = 0;
 	u32 ret = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
 
-	xstate_bv &= ~XSTATE_FPSSE;
+	xstate_bv &= XSTATE_EXTEND_MASK;
 	while (xstate_bv) {
 		if (xstate_bv & 0x1) {
 		        u32 eax, ebx, ecx, edx;
···
 		vcpu->arch.guest_supported_xcr0 =
 			(best->eax | ((u64)best->edx << 32)) &
 			host_xcr0 & KVM_SUPPORTED_XCR0;
-		vcpu->arch.guest_xstate_size =
-			xstate_required_size(vcpu->arch.guest_supported_xcr0);
+		vcpu->arch.guest_xstate_size = best->ebx =
+			xstate_required_size(vcpu->arch.xcr0);
 	}
 
 	kvm_pmu_cpuid_update(vcpu);

arch/x86/kvm/x86.c

···
 
 int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 {
-	u64 xcr0;
+	u64 xcr0 = xcr;
+	u64 old_xcr0 = vcpu->arch.xcr0;
 	u64 valid_bits;
 
 	/* Only support XCR_XFEATURE_ENABLED_MASK(xcr0) now  */
 	if (index != XCR_XFEATURE_ENABLED_MASK)
 		return 1;
-	xcr0 = xcr;
 	if (!(xcr0 & XSTATE_FP))
 		return 1;
 	if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE))
···
 
 	kvm_put_guest_xcr0(vcpu);
 	vcpu->arch.xcr0 = xcr0;
+
+	if ((xcr0 ^ old_xcr0) & XSTATE_EXTEND_MASK)
+		kvm_update_cpuid(vcpu);
 	return 0;
 }