From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Fri, 25 Mar 2022 14:21:40 +0100
Subject: KVM: x86: Forbid VMM to set SYNIC/STIMER MSRs when SynIC wasn't
activated
Git-commit: b1e34d325397a33d97d845e312d7cf2a8b646b44
Patch-mainline: v5.18-rc1
References: bsc#1200788 CVE-2022-2153
Setting non-zero values to SYNIC/STIMER MSRs activates certain features,
this should not happen when KVM_CAP_HYPERV_SYNIC{,2} was not activated.
Note, it would've been better to forbid writing anything to SYNIC/STIMER
MSRs, including zeroes, however, at least QEMU tries clearing
HV_X64_MSR_STIMER0_CONFIG without SynIC. HV_X64_MSR_EOM MSR is somewhat
'special' as writing zero there triggers an action, this also should not
happen when SynIC wasn't activated.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220325132140.25650-4-vkuznets@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Dario Faggioli <dfaggioli@suse.com>
---
arch/x86/kvm/hyperv.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -214,7 +214,7 @@
struct kvm_vcpu *vcpu = synic_to_vcpu(synic);
int ret;
- if (!synic->active && !host)
+ if (!synic->active && (!host || data))
return 1;
trace_kvm_hv_synic_set_msr(vcpu->vcpu_id, msr, data, host);
@@ -260,6 +260,9 @@
case HV_X64_MSR_EOM: {
int i;
+ if (!synic->active)
+ break;
+
for (i = 0; i < ARRAY_SIZE(synic->sint); i++)
kvm_hv_notify_acked_sint(vcpu, i);
break;
@@ -526,7 +529,7 @@
struct kvm_vcpu *vcpu = stimer_to_vcpu(stimer);
struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu);
- if (!synic->active && !host)
+ if (!synic->active && (!host || config))
return 1;
trace_kvm_hv_stimer_set_config(stimer_to_vcpu(stimer)->vcpu_id,
@@ -549,7 +552,7 @@
struct kvm_vcpu *vcpu = stimer_to_vcpu(stimer);
struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu);
- if (!synic->active && !host)
+ if (!synic->active && (!host || count))
return 1;
trace_kvm_hv_stimer_set_count(stimer_to_vcpu(stimer)->vcpu_id,