From patchwork Wed Apr 8 06:40:58 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 11479459 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 4881B92C for ; Wed, 8 Apr 2020 06:41:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 25FBD2072A for ; Wed, 8 Apr 2020 06:41:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726605AbgDHGlB (ORCPT ); Wed, 8 Apr 2020 02:41:01 -0400 Received: from mga11.intel.com ([192.55.52.93]:58629 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725763AbgDHGlA (ORCPT ); Wed, 8 Apr 2020 02:41:00 -0400 IronPort-SDR: hsczhdo64+ePuI3P9IvcPEUFAHM8AdfFwQcNPeyKNXKD96mw9Fo2SRih1kHhhuGxdU/+cuM9/o H5NatOmDDERA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Apr 2020 23:41:00 -0700 IronPort-SDR: kXTd4oDxUKWyEoclSVSNSkdaL7KhEVHfzJ6FUtRw0GL2tAO7pgYelG74re22M+/MIRlGlIw1Ha U+zWgrp/r1OQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,357,1580803200"; d="scan'208";a="240207984" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.202]) by orsmga007.jf.intel.com with ESMTP; 07 Apr 2020 23:40:59 -0700 From: Sean Christopherson To: Christian Borntraeger , Janosch Frank , Paolo Bonzini Cc: David Hildenbrand , Cornelia Huck , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+d889b59b2bb87d4047a2@syzkaller.appspotmail.com Subject: [PATCH 1/2] KVM: Check validity of resolved slot when searching memslots Date: Tue, 7 Apr 2020 23:40:58 -0700 Message-Id: <20200408064059.8957-2-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200408064059.8957-1-sean.j.christopherson@intel.com> References: <20200408064059.8957-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Check that the resolved slot (somewhat confusingly named 'start') is a valid/allocated slot before doing the final comparison to see if the specified gfn resides in the associated slot. The resolved slot can be invalid if the binary search loop terminated because the search index was incremented beyond the number of used slots. This bug has existed since the binary search algorithm was introduced, but went unnoticed because KVM statically allocated memory for the max number of slots, i.e. the access would only be truly out-of-bounds if all possible slots were allocated and the specified gfn was less than the base of the lowest memslot. Commit 36947254e5f98 ("KVM: Dynamically size memslot array based on number of used slots") eliminated the "all possible slots allocated" condition and made the bug embarrasingly easy to hit. Fixes: 9c1a5d38780e6 ("kvm: optimize GFN to memslot lookup with large slots amount") Reported-by: syzbot+d889b59b2bb87d4047a2@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Reviewed-by: Cornelia Huck --- include/linux/kvm_host.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 6d58beb65454..01276e3d01b9 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -1048,7 +1048,7 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn) start = slot + 1; } - if (gfn >= memslots[start].base_gfn && + if (start < slots->used_slots && gfn >= memslots[start].base_gfn && gfn < memslots[start].base_gfn + memslots[start].npages) { atomic_set(&slots->lru_slot, start); return &memslots[start];