From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EE380C4167B for ; Tue, 12 Apr 2022 09:11:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1359287AbiDLJKn (ORCPT ); Tue, 12 Apr 2022 05:10:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55294 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1358947AbiDLHmW (ORCPT ); Tue, 12 Apr 2022 03:42:22 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0F17554BD0; Tue, 12 Apr 2022 00:19:41 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 471AEB81B67; Tue, 12 Apr 2022 07:19:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98439C385AB; Tue, 12 Apr 2022 07:19:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649747979; bh=NwKPkCap+dw1eHh5siCsbaMYWMopuS5/YjbGJCk9bjU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RhUfw83NFvDBuor1kGzeItLgEXEWaOwYyu7aDS7LNxzhDA4VLnvSviJcM29UcB0zc enNNGNAN1z4ESJG17xG23dhuOxNSgPEUf75u2qoYeMqsEIuu6jkf+EtJreC5cGp7ZO 7j3rvPdDa2bq730mNt47Vzpk6MV9C8xMbYmUv5eI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+6bde52d89cfdf9f61425@syzkaller.appspotmail.com, Paolo Bonzini , Sean Christopherson , Andrew Morton , Linus Torvalds Subject: [PATCH 5.17 274/343] mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) Date: Tue, 12 Apr 2022 08:31:32 +0200 Message-Id: <20220412062959.231328521@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220412062951.095765152@linuxfoundation.org> References: <20220412062951.095765152@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Paolo Bonzini commit 01e67e04c28170c47700c2c226d732bbfedb1ad0 upstream. If an mremap() syscall with old_size=0 ends up in move_page_tables(), it will call invalidate_range_start()/invalidate_range_end() unnecessarily, i.e. with an empty range. This causes a WARN in KVM's mmu_notifier. In the past, empty ranges have been diagnosed to be off-by-one bugs, hence the WARNing. Given the low (so far) number of unique reports, the benefits of detecting more buggy callers seem to outweigh the cost of having to fix cases such as this one, where userspace is doing something silly. In this particular case, an early return from move_page_tables() is enough to fix the issue. Link: https://lkml.kernel.org/r/20220329173155.172439-1-pbonzini@redhat.com Reported-by: syzbot+6bde52d89cfdf9f61425@syzkaller.appspotmail.com Signed-off-by: Paolo Bonzini Cc: Sean Christopherson Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/mremap.c | 3 +++ 1 file changed, 3 insertions(+) --- a/mm/mremap.c +++ b/mm/mremap.c @@ -486,6 +486,9 @@ unsigned long move_page_tables(struct vm pmd_t *old_pmd, *new_pmd; pud_t *old_pud, *new_pud; + if (!len) + return 0; + old_end = old_addr + len; flush_cache_range(vma, old_addr, old_end);