KVM: SVM: Skip VMSA init in sev_es_init_vmcb() if pointer is NULL

commit 1952e74da96fb3e48b72a2d0ece78c688a5848c1 upstream.

Skip initializing the VMSA physical address in the VMCB if the VMSA is
NULL, which occurs during intrahost migration as KVM initializes the VMCB
before copying over state from the source to the destination (including
the VMSA and its physical address).

In normal builds, __pa() is just math, so the bug isn't fatal, but with
CONFIG_DEBUG_VIRTUAL=y, the validity of the virtual address is verified
and passing in NULL will make the kernel unhappy.

Fixes: 6defa24d3b12 ("KVM: SEV: Init target VMCBs in sev_migrate_from")
Cc: stable@vger.kernel.org
Cc: Peter Gonda <pgonda@google.com>
Reviewed-by: Peter Gonda <pgonda@google.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Link: https://lore.kernel.org/r/20230825022357.2852133-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 9a1fa28443ae5c781f2f23734ed9c9d2ce40c15c..d08d5e085649faed355919bb159ea4d95c2a175b 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2951,9 +2951,12 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
        /*
         * An SEV-ES guest requires a VMSA area that is a separate from the
         * VMCB page. Do not include the encryption mask on the VMSA physical
-        * address since hardware will access it using the guest key.
+        * address since hardware will access it using the guest key.  Note,
+        * the VMSA will be NULL if this vCPU is the destination for intrahost
+        * migration, and will be copied later.
         */
-       svm->vmcb->control.vmsa_pa = __pa(svm->sev_es.vmsa);
+       if (svm->sev_es.vmsa)
+               svm->vmcb->control.vmsa_pa = __pa(svm->sev_es.vmsa);
 
        /* Can't intercept CR register access, HV can't modify CR registers */
        svm_clr_intercept(svm, INTERCEPT_CR0_READ);