KVM: s390: vsie: Fix STFLE interpretive execution identification

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: 66b630d ("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>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20231219140854.1042599-2-nsg@linux.ibm.com
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Message-ID: <20231219140854.1042599-2-nsg@linux.ibm.com>

Author: Nina Schoetterl-Glausch

arch/s390/kvm/vsie.c

@@ -988,10 +988,15 @@ 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);