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 X-Spam-Level: X-Spam-Status: No, score=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A2E2BC5517A for ; Wed, 11 Nov 2020 15:43:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F9D720729 for ; Wed, 11 Nov 2020 15:43:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="P+KZjJwQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727438AbgKKPnw (ORCPT ); Wed, 11 Nov 2020 10:43:52 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:31575 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727424AbgKKPnv (ORCPT ); Wed, 11 Nov 2020 10:43:51 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1605109429; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=bw81PsEaDm3tUnrsxO8Odvn+M+fX2gNDcSxC7Tq7e6A=; b=P+KZjJwQLOZXyCACtUSBcN9c4R4M9APFn4aRKk482nnGnADx0SO4OyQJKNtHIv81ULeitS 3on+HuwfZvojO0DnNBnIkuXDNs62e+XTBZ3Mp4jRwc03OPLRpPn0CPBzJZMGCn3IGxUI44 qJd2oONQ2mtxf8NwfxwN7zPUiSGQfo4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-316-u64_rxA9Pp-OJsGC2d_Qnw-1; Wed, 11 Nov 2020 10:43:47 -0500 X-MC-Unique: u64_rxA9Pp-OJsGC2d_Qnw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4FEDC188C126; Wed, 11 Nov 2020 15:43:46 +0000 (UTC) Received: from [10.36.114.151] (ovpn-114-151.ams2.redhat.com [10.36.114.151]) by smtp.corp.redhat.com (Postfix) with ESMTP id 632EA27BC2; Wed, 11 Nov 2020 15:43:44 +0000 (UTC) Subject: Re: [PATCH v2 4/5] mm, page_poison: remove CONFIG_PAGE_POISONING_NO_SANITY To: Vlastimil Babka , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alexander Potapenko , Kees Cook , Michal Hocko , Mateusz Nosek , Laura Abbott References: <20201103152237.9853-1-vbabka@suse.cz> <20201103152237.9853-5-vbabka@suse.cz> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <3c331f29-bbbe-709f-a1e3-a3710bbac5ad@redhat.com> Date: Wed, 11 Nov 2020 16:43:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20201103152237.9853-5-vbabka@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03.11.20 16:22, Vlastimil Babka wrote: > CONFIG_PAGE_POISONING_NO_SANITY skips the check on page alloc whether the > poison pattern was corrupted, suggesting a use-after-free. The motivation to > introduce it in commit 8823b1dbc05f ("mm/page_poison.c: enable PAGE_POISONING > as a separate option") was to simply sanitize freed pages, optimally together > with CONFIG_PAGE_POISONING_ZERO. > > These days we have an init_on_free=1 boot option, which makes this use case of > page poisoning redundant. For sanitizing, writing zeroes is sufficient, there > is pretty much no benefit from writing the 0xAA poison pattern to freed pages, > without checking it back on alloc. Thus, remove this option and suggest > init_on_free instead in the main config's help. > > Signed-off-by: Vlastimil Babka > --- > drivers/virtio/virtio_balloon.c | 4 +--- > mm/Kconfig.debug | 15 ++++----------- > mm/page_poison.c | 3 --- > 3 files changed, 5 insertions(+), 17 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index e53faed6ba93..8985fc2cea86 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -1114,9 +1114,7 @@ static int virtballoon_validate(struct virtio_device *vdev) > * page reporting as it could potentially change the contents > * of our free pages. > */ > - if (!want_init_on_free() && > - (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) || > - !page_poisoning_enabled_static())) > + if (!want_init_on_free() && !page_poisoning_enabled_static()) > __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); > else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) > __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); > diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug > index c57786ad5be9..14e29fe5bfa6 100644 > --- a/mm/Kconfig.debug > +++ b/mm/Kconfig.debug > @@ -74,18 +74,11 @@ config PAGE_POISONING > Note that "poison" here is not the same thing as the "HWPoison" > for CONFIG_MEMORY_FAILURE. This is software poisoning only. > > - If unsure, say N > + If you are only interested in sanitization of freed pages without > + checking the poison pattern on alloc, you can boot the kernel with > + "init_on_free=1" instead of enabling this. > > -config PAGE_POISONING_NO_SANITY > - depends on PAGE_POISONING > - bool "Only poison, don't sanity check" > - help > - Skip the sanity checking on alloc, only fill the pages with > - poison on free. This reduces some of the overhead of the > - poisoning feature. > - > - If you are only interested in sanitization, say Y. Otherwise > - say N. > + If unsure, say N > > config PAGE_POISONING_ZERO > bool "Use zero for poisoning instead of debugging value" > diff --git a/mm/page_poison.c b/mm/page_poison.c > index dd7aeada036f..084fc3ff4c15 100644 > --- a/mm/page_poison.c > +++ b/mm/page_poison.c > @@ -51,9 +51,6 @@ static void check_poison_mem(unsigned char *mem, size_t bytes) > unsigned char *start; > unsigned char *end; > > - if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY)) > - return; > - > start = memchr_inv(mem, PAGE_POISON, bytes); > if (!start) > return; > This clearly simplifies things. Acked-by: David Hildenbrand -- Thanks, David / dhildenb