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

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Am 19.12.23 um 15:08 schrieb Nina Schoetterl-Glausch:
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@xxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Nina Schoetterl-Glausch <nsg@xxxxxxxxxxxxx>

Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>

this should not matter in reality but maybe some weird guests puts this at address 0.
Do we want a unit test for that case?

---
  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);




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