[PATCH 2/2] KVM: s390: Return last valid slot if approx index is out-of-bounds

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: David Hildenbrand <david@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	syzbot+d889b59b2bb87d4047a2@syzkaller.appspotmail.com
Subject: [PATCH 2/2] KVM: s390: Return last valid slot if approx index is out-of-bounds
Date: Tue,  7 Apr 2020 23:40:59 -0700	[thread overview]
Message-ID: <20200408064059.8957-3-sean.j.christopherson@intel.com> (raw)
In-Reply-To: <20200408064059.8957-1-sean.j.christopherson@intel.com>

Return the index of the last valid slot from gfn_to_memslot_approx() if
its binary search loop yielded an out-of-bounds index.  The index can
be out-of-bounds if the specified gfn is less than the base of the
lowest memslot (which is also the last valid memslot).

Note, the sole caller, kvm_s390_get_cmma(), ensures used_slots is
non-zero.

Fixes: afdad61615cc3 ("KVM: s390: Fix storage attributes migration with memory slots")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/s390/kvm/kvm-s390.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 19a81024fe16..5dcf9ff12828 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1939,6 +1939,9 @@ static int gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn)
 			start = slot + 1;
 	}
 
+	if (start >= slots->used_slots)
+		return slots->used_slots - 1;
+
 	if (gfn >= memslots[start].base_gfn &&
 	    gfn < memslots[start].base_gfn + memslots[start].npages) {
 		atomic_set(&slots->lru_slot, start);
-- 
2.24.1

