KVM: x86: fix KVM_SET_XCRS for CPUs that do not support XSAVE

The KVM_SET_XCRS ioctl must accept anything that KVM_GET_XCRS
could return.  XCR0's bit 0 is always 1 in real processors with
XSAVE, and KVM_GET_XCRS will always leave bit 0 set even if the
emulated processor does not have XSAVE.  So, KVM_SET_XCRS must
ignore that bit when checking for attempts to enable unsupported
save states.

Reviewed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ec35d09937da..296154956399 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -577,6 +577,7 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
 int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 {
         u64 xcr0;
+        u64 valid_bits;
 
         /* Only support XCR_XFEATURE_ENABLED_MASK(xcr0) now  */
         if (index != XCR_XFEATURE_ENABLED_MASK)
@@ -586,8 +587,16 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
                 return 1;
         if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE))
                 return 1;
-        if (xcr0 & ~vcpu->arch.guest_supported_xcr0)
+
+        /*
+         * Do not allow the guest to set bits that we do not support
+         * saving.  However, xcr0 bit 0 is always set, even if the
+         * emulated CPU does not support XSAVE (see fx_init).
+         */
+        valid_bits = vcpu->arch.guest_supported_xcr0 | XSTATE_FP;
+        if (xcr0 & ~valid_bits)
                 return 1;
+
         kvm_put_guest_xcr0(vcpu);
         vcpu->arch.xcr0 = xcr0;
         return 0;