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=-12.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 EC1C3C388F9 for ; Tue, 3 Nov 2020 15:26:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ADFF62072D for ; Tue, 3 Nov 2020 15:26:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728198AbgKCPZI (ORCPT ); Tue, 3 Nov 2020 10:25:08 -0500 Received: from mx2.suse.de ([195.135.220.15]:51660 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728180AbgKCPWw (ORCPT ); Tue, 3 Nov 2020 10:22:52 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 70F0BACB5; Tue, 3 Nov 2020 15:22:50 +0000 (UTC) From: Vlastimil Babka To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alexander Potapenko , Kees Cook , Michal Hocko , David Hildenbrand , Mateusz Nosek , Laura Abbott , Vlastimil Babka Subject: [PATCH v2 4/5] mm, page_poison: remove CONFIG_PAGE_POISONING_NO_SANITY Date: Tue, 3 Nov 2020 16:22:36 +0100 Message-Id: <20201103152237.9853-5-vbabka@suse.cz> X-Mailer: git-send-email 2.29.1 In-Reply-To: <20201103152237.9853-1-vbabka@suse.cz> References: <20201103152237.9853-1-vbabka@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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; -- 2.29.1