KVM: SEV: Allow some commands for mirror VM

A mirrored SEV-ES VM will need to call KVM_SEV_LAUNCH_UPDATE_VMSA to
setup its vCPUs and have them measured, and their VMSAs encrypted. Without
this change, it is impossible to have mirror VMs as part of SEV-ES VMs.

Also allow the guest status check and debugging commands since they do
not change any guest state.

Signed-off-by: Peter Gonda <pgonda@google.com>
Cc: Marc Orr <marcorr@google.com>
Cc: Nathan Tempelman <natet@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Steve Rutherford <srutherford@google.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: 54526d1fd593 ("KVM: x86: Support KVM VMs sharing SEV context", 2021-04-21)
Message-Id: <20210921150345.2221634-3-pgonda@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 5ec10ed..c36b5fe 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1510,6 +1510,20 @@ static int sev_receive_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
        return sev_issue_cmd(kvm, SEV_CMD_RECEIVE_FINISH, &data, &argp->error);
 }
 
+static bool cmd_allowed_from_miror(u32 cmd_id)
+{
+       /*
+        * Allow mirrors VM to call KVM_SEV_LAUNCH_UPDATE_VMSA to enable SEV-ES
+        * active mirror VMs. Also allow the debugging and status commands.
+        */
+       if (cmd_id == KVM_SEV_LAUNCH_UPDATE_VMSA ||
+           cmd_id == KVM_SEV_GUEST_STATUS || cmd_id == KVM_SEV_DBG_DECRYPT ||
+           cmd_id == KVM_SEV_DBG_ENCRYPT)
+               return true;
+
+       return false;
+}
+
 int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 {
        struct kvm_sev_cmd sev_cmd;
@@ -1526,8 +1540,9 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
 
        mutex_lock(&kvm->lock);
 
-       /* enc_context_owner handles all memory enc operations */
-       if (is_mirroring_enc_context(kvm)) {
+       /* Only the enc_context_owner handles some memory enc operations. */
+       if (is_mirroring_enc_context(kvm) &&
+           !cmd_allowed_from_miror(sev_cmd.id)) {
                r = -EINVAL;
                goto out;
        }