[PATCH] KVM: SVM: Make sure GHCB is mapped before updating

[Tom Lendacky <thomas.lendacky@amd.com>]

From: Tom Lendacky <thomas.lendacky@amd.com>

The sev_vcpu_deliver_sipi_vector() routine will update the GHCB to inform
the caller of the AP Reset Hold NAE event that a SIPI has been delivered.
However, if a SIPI is performed without a corresponding AP Reset Hold,
then the GHCB may not be mapped, which will result in a NULL pointer
dereference.

Check that the GHCB is mapped before attempting the update.

Fixes: 647daca25d24 ("KVM: SVM: Add support for booting APs in an SEV-ES guest")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/kvm/svm/sev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 83e00e524513..13758e3b106d 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2105,5 +2105,6 @@ void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
 	 * the guest will set the CS and RIP. Set SW_EXIT_INFO_2 to a
 	 * non-zero value.
 	 */
-	ghcb_set_sw_exit_info_2(svm->ghcb, 1);
+	if (svm->ghcb)
+		ghcb_set_sw_exit_info_2(svm->ghcb, 1);
 }
-- 
2.31.0