linux-kernel - [PATCH 3.2 006/102] KVM: s390: Fix user triggerable bug in dead code

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Message-ID: <lsq.1414880883.728071678@decadent.org.uk>
Date:	Sat, 01 Nov 2014 22:28:03 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"David Hildenbrand" <dahi@...ux.vnet.ibm.com>,
	"Cornelia Huck" <cornelia.huck@...ibm.com>,
	"Christian Borntraeger" <borntraeger@...ibm.com>
Subject: [PATCH 3.2 006/102] KVM: s390: Fix user triggerable bug in dead code

3.2.64-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Borntraeger <borntraeger@...ibm.com>

commit 614a80e474b227cace52fd6e3c790554db8a396e upstream.

In the early days, we had some special handling for the
KVM_EXIT_S390_SIEIC exit, but this was gone in 2009 with commit
d7b0b5eb3000 (KVM: s390: Make psw available on all exits, not
just a subset).

Now this switch statement is just a sanity check for userspace
not messing with the kvm_run structure. Unfortunately, this
allows userspace to trigger a kernel BUG. Let's just remove
this switch statement.

Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@...ibm.com>
Reviewed-by: David Hildenbrand <dahi@...ux.vnet.ibm.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/s390/kvm/kvm-s390.c | 13 -------------
 1 file changed, 13 deletions(-)

--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -516,16 +516,6 @@ rerun_vcpu:
 
 	BUG_ON(vcpu->kvm->arch.float_int.local_int[vcpu->vcpu_id] == NULL);
 
-	switch (kvm_run->exit_reason) {
-	case KVM_EXIT_S390_SIEIC:
-	case KVM_EXIT_UNKNOWN:
-	case KVM_EXIT_INTR:
-	case KVM_EXIT_S390_RESET:
-		break;
-	default:
-		BUG();
-	}
-
 	vcpu->arch.sie_block->gpsw.mask = kvm_run->psw_mask;
 	vcpu->arch.sie_block->gpsw.addr = kvm_run->psw_addr;
 

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