KVM: x86: prevent setting unsupported XSAVE states

A guest can still attempt to save and restore XSAVE states even if they
have been masked in CPUID leaf 0Dh.  This usually is not visible to
the guest, but is still wrong: "Any attempt to set a reserved bit (as
determined by the contents of EAX and EDX after executing CPUID with
EAX=0DH, ECX= 0H) in XCR0 for a given processor will result in a #GP
exception".

The patch also performs the same checks as __kvm_set_xcr in KVM_SET_XSAVE.
This catches migration from newer to older kernel/processor before the
guest starts running.

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

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index c76ff74a98f2ed5ffcd72b4dcefbcb0c9203c0cd..35d10d1a6b58d5b703ac3aa1176e44438c6a1eb5 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -389,6 +389,7 @@ struct kvm_vcpu_arch {
 
        struct fpu guest_fpu;
        u64 xcr0;
+       u64 guest_supported_xcr0;
 
        struct kvm_pio_request pio;
        void *pio_data;

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index a03a9faf81b08a7bf403116f1adf28e23cb8ff00..5a5ff94fef652fecc9bedfd56e46fefbb4d5352b 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -46,6 +46,14 @@ void kvm_update_cpuid(struct kvm_vcpu *vcpu)
                        apic->lapic_timer.timer_mode_mask = 1 << 17;
        }
 
+       best = kvm_find_cpuid_entry(vcpu, 0xD, 0);
+       if (!best)
+               vcpu->arch.guest_supported_xcr0 = 0;
+       else
+               vcpu->arch.guest_supported_xcr0 =
+                       (best->eax | ((u64)best->edx << 32)) &
+                       host_xcr0 & KVM_SUPPORTED_XCR0;
+
        kvm_pmu_cpuid_update(vcpu);
 }
 

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 187f824b1454c948d259acf5e7e1c724e4be516b..7d5c5207a414d1144c18eac33d6c63ba2669b10c 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -586,7 +586,7 @@ 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 & ~host_xcr0)
+       if (xcr0 & ~vcpu->arch.guest_supported_xcr0)
                return 1;
        kvm_put_guest_xcr0(vcpu);
        vcpu->arch.xcr0 = xcr0;
@@ -3003,10 +3003,19 @@ static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
        u64 xstate_bv =
                *(u64 *)&guest_xsave->region[XSAVE_HDR_OFFSET / sizeof(u32)];
 
-       if (cpu_has_xsave)
+       if (cpu_has_xsave) {
+               /*
+                * Here we allow setting states that are not present in
+                * CPUID leaf 0xD, index 0, EDX:EAX.  This is for compatibility
+                * with old userspace.
+                */
+               if (xstate_bv & ~KVM_SUPPORTED_XCR0)
+                       return -EINVAL;
+               if (xstate_bv & ~host_xcr0)
+                       return -EINVAL;
                memcpy(&vcpu->arch.guest_fpu.state->xsave,
                        guest_xsave->region, xstate_size);
-       else {
+       } else {
                if (xstate_bv & ~XSTATE_FPSSE)
                        return -EINVAL;
                memcpy(&vcpu->arch.guest_fpu.state->fxsave,
@@ -6940,6 +6949,9 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 
        vcpu->arch.ia32_tsc_adjust_msr = 0x0;
        vcpu->arch.pv_time_enabled = false;
+
+       vcpu->arch.guest_supported_xcr0 = 0;
+
        kvm_async_pf_hash_reset(vcpu);
        kvm_pmu_init(vcpu);