From patchwork Thu Apr 14 13:13:53 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 561538 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 60043C433FE for ; Thu, 14 Apr 2022 14:12:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345271AbiDNONj (ORCPT ); Thu, 14 Apr 2022 10:13:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43184 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347644AbiDNN7Z (ORCPT ); Thu, 14 Apr 2022 09:59:25 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2A344614B; Thu, 14 Apr 2022 06:50:51 -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 77200B82910; Thu, 14 Apr 2022 13:50:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C3294C385A1; Thu, 14 Apr 2022 13:50:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649944249; bh=3VVivc/RhCqCrHRTKMJ3oOfid8dXSDmtwK7BdwPjUmY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hMV8Xeo7vE4SfFWG7DySxxjiVG66rGOI9dk1qBPr42yx+l8O0zDhWFjMcSDbG0tgO 5qUwIofWwGXVNa2ehRNHRntgotm1E1DrO9oVzJ2niSTBLy9gVrSlWMC3reN6bF0bqy u0osWSy+4GYG1MUeKlgmmCAOLfJwR2vunMSJPE6o= 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 5.4 448/475] mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) Date: Thu, 14 Apr 2022 15:13:53 +0200 Message-Id: <20220414110907.595867115@linuxfoundation.org> X-Mailer: git-send-email 2.35.2 In-Reply-To: <20220414110855.141582785@linuxfoundation.org> References: <20220414110855.141582785@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@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 @@ -246,6 +246,9 @@ unsigned long move_page_tables(struct vm struct mmu_notifier_range range; pmd_t *old_pmd, *new_pmd; + if (!len) + return 0; + old_end = old_addr + len; flush_cache_range(vma, old_addr, old_end);