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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 A2FE8C433DF for ; Tue, 2 Jun 2020 14:16:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 840C220878 for ; Tue, 2 Jun 2020 14:16:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728313AbgFBOQR (ORCPT ); Tue, 2 Jun 2020 10:16:17 -0400 Received: from mx2.suse.de ([195.135.220.15]:43068 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728162AbgFBOQM (ORCPT ); Tue, 2 Jun 2020 10:16:12 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id B9707AE69; Tue, 2 Jun 2020 14:16:12 +0000 (UTC) From: Vlastimil Babka To: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, vinmenon@codeaurora.org, Kees Cook , Matthew Garrett , Vlastimil Babka , Jann Horn , Vijayanand Jitta Subject: [RFC PATCH 3/5] mm, slub: remove runtime allocation order changes Date: Tue, 2 Jun 2020 16:15:17 +0200 Message-Id: <20200602141519.7099-4-vbabka@suse.cz> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200602141519.7099-1-vbabka@suse.cz> References: <20200602141519.7099-1-vbabka@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org SLUB allows runtime changing of page allocation order by writing into the /sys/kernel/slab//order file. Jann has reported [1] that this interface allows the order to be set too small, leading to crashes. While it's possible to fix the immediate issue, closer inspection reveals potential races. Storing the new order calls calculate_sizes() which non-atomically updates a lot of kmem_cache fields while the cache is still in use. Unexpected behavior might occur even if the fields are set to the same value as they were. This could be fixed by splitting out the part of calculate_sizes() that depends on forced_order, so that we only update kmem_cache.oo field. This could still race with init_cache_random_seq(), shuffle_freelist(), allocate_slab(). Perhaps it's possible to audit and e.g. add some READ_ONCE/WRITE_ONCE accesses, it might be easier just to remove the runtime order changes, which is what this patch does. If there are valid usecases for per-cache order setting, we could e.g. extend the boot parameters to do that. [1] https://lore.kernel.org/r/CAG48ez31PP--h6_FzVyfJ4H86QYczAFPdxtJHUEEan+7VJETAQ@mail.gmail.com Reported-by: Jann Horn Signed-off-by: Vlastimil Babka --- mm/slub.c | 19 +------------------ 1 file changed, 1 insertion(+), 18 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index ac198202dbb0..58c1e9e7b3b3 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5111,28 +5111,11 @@ static ssize_t objs_per_slab_show(struct kmem_cache *s, char *buf) } SLAB_ATTR_RO(objs_per_slab); -static ssize_t order_store(struct kmem_cache *s, - const char *buf, size_t length) -{ - unsigned int order; - int err; - - err = kstrtouint(buf, 10, &order); - if (err) - return err; - - if (order > slub_max_order || order < slub_min_order) - return -EINVAL; - - calculate_sizes(s, order); - return length; -} - static ssize_t order_show(struct kmem_cache *s, char *buf) { return sprintf(buf, "%u\n", oo_order(s->oo)); } -SLAB_ATTR(order); +SLAB_ATTR_RO(order); static ssize_t min_partial_show(struct kmem_cache *s, char *buf) { -- 2.26.2