Patch "KVM: s390: fix memory overwrites when not using SCA entries" has been added to the 4.15-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    KVM: s390: fix memory overwrites when not using SCA entries

to the 4.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-s390-fix-memory-overwrites-when-not-using-sca-entries.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From f07afa0462b76a5b9c4f3a43d5ac24fdb86a90c2 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@redhat.com>
Date: Tue, 6 Mar 2018 14:27:58 +0100
Subject: KVM: s390: fix memory overwrites when not using SCA entries

From: David Hildenbrand <david@redhat.com>

commit f07afa0462b76a5b9c4f3a43d5ac24fdb86a90c2 upstream.

Even if we don't have extended SCA support, we can have more than 64 CPUs
if we don't enable any HW features that might use the SCA entries.

Now, this works just fine, but we missed a return, which is why we
would actually store the SCA entries. If we have more than 64 CPUs, this
means writing outside of the basic SCA - bad.

Let's fix this. This allows > 64 CPUs when running nested (under vSIE)
without random crashes.

Fixes: a6940674c384 ("KVM: s390: allow 255 VCPUs when sca entries aren't used")
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180306132758.21034-1-david@redhat.com>
Cc: stable@vger.kernel.org
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/s390/kvm/kvm-s390.c |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2118,6 +2118,7 @@ static void sca_add_vcpu(struct kvm_vcpu
 		/* we still need the basic sca for the ipte control */
 		vcpu->arch.sie_block->scaoh = (__u32)(((__u64)sca) >> 32);
 		vcpu->arch.sie_block->scaol = (__u32)(__u64)sca;
+		return;
 	}
 	read_lock(&vcpu->kvm->arch.sca_lock);
 	if (vcpu->kvm->arch.use_esca) {


Patches currently in stable-queue which might be from david@redhat.com are

queue-4.15/kvm-s390-fix-memory-overwrites-when-not-using-sca-entries.patch