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 c76ff74..35d10d1 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -389,6 +389,7 @@
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 a03a9fa..5a5ff94 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -46,6 +46,14 @@
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 187f824..7d5c520 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -586,7 +586,7 @@
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 @@
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 @@
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);