kvm: svm: Fix gctx page leak on invalid inputs

Ensure that snp gctx page allocation is adequately deallocated on
failure during snp_launch_start.

Fixes: 136d8bc ("KVM: SEV: Add KVM_SEV_SNP_LAUNCH_START command")

CC: Sean Christopherson <[email protected]>
CC: Paolo Bonzini <[email protected]>
CC: Thomas Gleixner <[email protected]>
CC: Ingo Molnar <[email protected]>
CC: Borislav Petkov <[email protected]>
CC: Dave Hansen <[email protected]>
CC: Ashish Kalra <[email protected]>
CC: Tom Lendacky <[email protected]>
CC: John Allen <[email protected]>
CC: Herbert Xu <[email protected]>
CC: "David S. Miller" <[email protected]>
CC: Michael Roth <[email protected]>
CC: Luis Chamberlain <[email protected]>
CC: Russ Weight <[email protected]>
CC: Danilo Krummrich <[email protected]>
CC: Greg Kroah-Hartman <[email protected]>
CC: "Rafael J. Wysocki" <[email protected]>
CC: Tianfei zhang <[email protected]>
CC: Alexey Kardashevskiy <[email protected]>

Signed-off-by: Dionna Glaze <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: deeglaze

arch/x86/kvm/svm/sev.c

@@ -2215,10 +2215,6 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	if (sev->snp_context)
 		return -EINVAL;
 
-	sev->snp_context = snp_context_create(kvm, argp);
-	if (!sev->snp_context)
-		return -ENOTTY;
-
 	if (params.flags)
 		return -EINVAL;
 
@@ -2233,6 +2229,10 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	if (params.policy & SNP_POLICY_MASK_SINGLE_SOCKET)
 		return -EINVAL;
 
+	sev->snp_context = snp_context_create(kvm, argp);
+	if (!sev->snp_context)
+		return -ENOTTY;
+
 	start.gctx_paddr = __psp_pa(sev->snp_context);
 	start.policy = params.policy;
 	memcpy(start.gosvw, params.gosvw, sizeof(params.gosvw));