From patchwork Fri Apr 8 20:09:04 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 559178 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 62FA3C43219 for ; Fri, 8 Apr 2022 20:09:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239395AbiDHULQ (ORCPT ); Fri, 8 Apr 2022 16:11:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239412AbiDHULP (ORCPT ); Fri, 8 Apr 2022 16:11:15 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A8756353ABD; Fri, 8 Apr 2022 13:09:06 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 40D4261E3D; Fri, 8 Apr 2022 20:09:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 943B7C385A5; Fri, 8 Apr 2022 20:09:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1649448545; bh=Uwe61k3TCdIIAb9jWMhOFX99NiRwkoxxsB+Q7xD3Mck=; h=Date:To:From:In-Reply-To:Subject:From; b=vP/PnsHIBa1QkY85u2AzCWADg8BR56BgOHgbNPxvhlodwAHV2uFg+4GZaQnYjzxR7 yTGwqWwXKwNBQeH/KgPabxhmHs3C/yGHkHOxAjQusbesROJyu/SMVuFs3OGvcXXsTI WxKEvc8QjUp4poAk0vPDkxfNm2Euhwq6YXdQ791g= Date: Fri, 08 Apr 2022 13:09:04 -0700 To: stable@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, akpm@linux-foundation.org, patches@lists.linux.dev, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org From: Andrew Morton In-Reply-To: <20220408130819.a89195e527ce58dfbe0700b9@linux-foundation.org> Subject: [patch 5/9] mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) Message-Id: <20220408200905.943B7C385A5@smtp.kernel.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Paolo Bonzini Subject: mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) 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 --- mm/mremap.c | 3 +++ 1 file changed, 3 insertions(+) --- a/mm/mremap.c~mm-avoid-pointless-invalidate_range_start-end-on-mremapold_size=0 +++ a/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);