[PATCH] KVM: SEV: Acquire vcpu mutex when updating VMSA

Peter Gonda
2021-09-14T20:06:48Z

Adds mutex guard to the VMSA updating code. Also adds a check to skip a
vCPU if it has already been LAUNCH_UPDATE_VMSA'd which should allow
userspace to retry this ioctl until all the vCPUs can be successfully
LAUNCH_UPDATE_VMSA'd. Because this operation cannot be undone we cannot
unwind if one vCPU fails.

Fixes: ad73109ae7ec ("KVM: SVM: Provide support to launch and run an SEV-ES guest")

Signed-off-by: Peter Gonda <pgonda@google.com>
Cc: Marc Orr <marcorr@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: kvm@vger.kernel.org
Cc: stable@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
arch/x86/kvm/svm/sev.c | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 75e0b21ad07c..9a2ebd0328ca 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -598,22 +598,29 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
{
struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
- struct sev_data_launch_update_vmsa vmsa;
+ struct sev_data_launch_update_vmsa vmsa = {0};
struct kvm_vcpu *vcpu;
int i, ret;

if (!sev_es_guest(kvm))
return -ENOTTY;

- vmsa.reserved = 0;
-
kvm_for_each_vcpu(i, vcpu, kvm) {
struct vcpu_svm *svm = to_svm(vcpu);

+ ret = mutex_lock_killable(&vcpu->mutex);
+ if (ret)
+ goto out_unlock;
+
+ /* Skip to the next vCPU if this one has already be updated. */
+ ret = sev_es_sync_vmsa(svm);
+ if (svm->vcpu.arch.guest_state_protected)
+ goto unlock;
+
/* Perform some pre-encryption checks against the VMSA */
ret = sev_es_sync_vmsa(svm);
if (ret)
- return ret;
+ goto out_unlock;

/*
* The LAUNCH_UPDATE_VMSA command will perform in-place
@@ -629,12 +636,19 @@ static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_VMSA, &vmsa,
&argp->error);
if (ret)
- return ret;
+ goto out_unlock;

svm->vcpu.arch.guest_state_protected = true;
+
+unlock:
+ mutex_unlock(&vcpu->mutex);
}

return 0;
+
+out_unlock:
+ mutex_unlock(&vcpu->mutex);
+ return ret;
}

static int sev_launch_measure(struct kvm *kvm, struct kvm_sev_cmd *argp)
--
2.33.0.464.g1972c5931b-goog