[PATCH v4 1/4] KVM: s390: vsie: Fix STFLE interpretive execution identification

[Nina Schoetterl-Glausch <nsg@linux.ibm.com>]

STFLE can be interpretively executed.
This occurs when the facility list designation is unequal to zero.
Perform the check before applying the address mask instead of after.

Fixes: 66b630d5b7f2 ("KVM: s390: vsie: support STFLE interpretation")
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
---
 arch/s390/kvm/vsie.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index 8207a892bbe2..35937911724e 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -984,10 +984,15 @@ static void retry_vsie_icpt(struct vsie_page *vsie_page)
 static int handle_stfle(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 {
 	struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
-	__u32 fac = READ_ONCE(vsie_page->scb_o->fac) & 0x7ffffff8U;
+	__u32 fac = READ_ONCE(vsie_page->scb_o->fac);
 
 	if (fac && test_kvm_facility(vcpu->kvm, 7)) {
 		retry_vsie_icpt(vsie_page);
+		/*
+		 * The facility list origin (FLO) is in bits 1 - 28 of the FLD
+		 * so we need to mask here before reading.
+		 */
+		fac = fac & 0x7ffffff8U;
 		if (read_guest_real(vcpu, fac, &vsie_page->fac,
 				    sizeof(vsie_page->fac)))
 			return set_validity_icpt(scb_s, 0x1090U);
-- 
2.40.1