[PATCH] KVM: SEV-ES: fix another issue with string I/O VMGEXITs

[Paolo Bonzini]

If the guest requests string I/O from the hypervisor via VMGEXIT,
SW_EXITINFO2 will contain the REP count.  However, sev_es_string_io
was incorrectly treating it as the size of the GHCB buffer in
bytes.

This fixes the "outsw" test in the experimental SEV tests of
kvm-unit-tests.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 7ed9abfe8e9f ("KVM: SVM: Support string IO operations for an SEV-ES guest")
Reported-by: Marc Orr <marcorr@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/svm/sev.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index e672493b5d8d..12d29d669cbc 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2579,11 +2579,16 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 
 int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in)
 {
-	if (!setup_vmgexit_scratch(svm, in, svm->vmcb->control.exit_info_2))
+	u32 bytes;
+
+	if (unlikely(check_mul_overflow(svm->vmcb->control.exit_info_2, size, &bytes)))
+		return -EINVAL;
+
+	if (!setup_vmgexit_scratch(svm, in, bytes))
 		return -EINVAL;
 
-	return kvm_sev_es_string_io(&svm->vcpu, size, port,
-				    svm->ghcb_sa, svm->ghcb_sa_len / size, in);
+	return kvm_sev_es_string_io(&svm->vcpu, size, port, svm->ghcb_sa,
+				    svm->vmcb->control.exit_info_2, in);
 }
 
 void sev_es_init_vmcb(struct vcpu_svm *svm)
-- 
2.27.0