linux-kernel - [PATCH v2 2/5] KVM: s390: vsie: Fix delivery of addressing exceptions

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Date:   Fri,  3 Apr 2020 17:30:47 +0200
From:   David Hildenbrand <david@...hat.com>
To:     kvm@...r.kernel.org
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        David Hildenbrand <david@...hat.com>, stable@...r.kernel.org
Subject: [PATCH v2 2/5] KVM: s390: vsie: Fix delivery of addressing exceptions

Whenever we get an -EFAULT, we failed to read in guest 2 physical
address space. Such addressing exceptions are reported via a program
intercept to the nested hypervisor.

We faked the intercept, we have to return to guest 2. Instead, right
now we would be returning -EFAULT from the intercept handler, eventually
crashing the VM.

Addressing exceptions can only happen if the g2->g3 page tables
reference invalid g2 addresses (say, either a table or the final page is
not accessible - so something that basically never happens in sane
environments.

Identified by manual code inspection.

Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization")
Cc: <stable@...r.kernel.org> # v4.8+
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 arch/s390/kvm/vsie.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index 076090f9e666..4f6c22d72072 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 		scb_s->iprcc = PGM_ADDRESSING;
 		scb_s->pgmilc = 4;
 		scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4);
+		rc = 1;
 	}
 	return rc;
 }
-- 
2.25.1