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 C762DC41535 for ; Tue, 12 Apr 2022 07:28:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354517AbiDLH00 (ORCPT ); Tue, 12 Apr 2022 03:26:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351655AbiDLHMu (ORCPT ); Tue, 12 Apr 2022 03:12:50 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 161E015708; Mon, 11 Apr 2022 23:51:00 -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 BA985B81B35; Tue, 12 Apr 2022 06:50:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 205DCC385A6; Tue, 12 Apr 2022 06:50:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649746257; bh=NwKPkCap+dw1eHh5siCsbaMYWMopuS5/YjbGJCk9bjU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1O9yb8C1YvNloXmOLVOalZd+lTRVSQK1XSCK/4QyDryCQJbGmep5FQBh8EWEVu1i0 o2EAln0PRfau0+LJK2Mq07PhU2GE3s1tqsKimJCPwNvC6D1xjJiKuOUvptv2JFy/aT BA1Lp9tNETWyc3MCbQqJVgJNQHqitbnIYYzq7QAI= 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 5.15 216/277] mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) Date: Tue, 12 Apr 2022 08:30:19 +0200 Message-Id: <20220412062948.291822180@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220412062942.022903016@linuxfoundation.org> References: <20220412062942.022903016@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);