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 14F96C47086 for ; Thu, 14 Apr 2022 14:02:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346873AbiDNN6F (ORCPT ); Thu, 14 Apr 2022 09:58:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58036 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344259AbiDNNb1 (ORCPT ); Thu, 14 Apr 2022 09:31:27 -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 B9A22E6; Thu, 14 Apr 2022 06:29:02 -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 7D022B82986; Thu, 14 Apr 2022 13:29:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DDD5DC385A5; Thu, 14 Apr 2022 13:28:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649942940; bh=cBmM5eMSCAjjmEck3uOO3XNupINSU0Q3msvBUXYe6V4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0AgVCIAPdnbvZm0MZW7ItsUd+ci3gLNCBdl9kqJmlH5gXVYzxnU34retWmwkscVc3 KEJ73V8nR/hdqqDywa2jo4J4b7mBNfq9vgJgs4lX09EKLYuY2ddANi3dxr1i6tXe1M z4oUQvja8namcyIymalnDW6qzjbN/fOjgfDxIln8= 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 4.19 315/338] mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) Date: Thu, 14 Apr 2022 15:13:38 +0200 Message-Id: <20220414110847.853715846@linuxfoundation.org> X-Mailer: git-send-email 2.35.2 In-Reply-To: <20220414110838.883074566@linuxfoundation.org> References: <20220414110838.883074566@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 @@ -201,6 +201,9 @@ unsigned long move_page_tables(struct vm unsigned long mmun_start; /* For mmu_notifiers */ unsigned long mmun_end; /* For mmu_notifiers */ + if (!len) + return 0; + old_end = old_addr + len; flush_cache_range(vma, old_addr, old_end);