linux-kernel - [PATCH AUTOSEL 4.9 23/23] KVM: s390: vsie: Fix delivery of addressing exceptions

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Message-Id: <20200418144405.10565-23-sashal@kernel.org>
Date:   Sat, 18 Apr 2020 10:44:05 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Sasha Levin <sashal@...nel.org>, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 23/23] KVM: s390: vsie: Fix delivery of addressing exceptions

From: David Hildenbrand <david@...hat.com>

[ Upstream commit 4d4cee96fb7a3cc53702a9be8299bf525be4ee98 ]

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.
the correct thing to do is to return 1 as rc == 1 is the internal
representation of "we have to go back into g2".

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>
Link: https://lore.kernel.org/r/20200403153050.20569-3-david@redhat.com
Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
[borntraeger@...ibm.com: fix patch description]
Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 da246d95b87c1..d3f046eca7db9 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -947,6 +947,7 @@ 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;
 }
-- 
2.20.1