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=-14.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 40CB5C2BA19 for ; Wed, 15 Apr 2020 18:08:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 020F5206D5 for ; Wed, 15 Apr 2020 18:08:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="DzHggght" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 020F5206D5 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BCAE28E0031; Wed, 15 Apr 2020 14:08:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B7C0E8E0001; Wed, 15 Apr 2020 14:08:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A913E8E0031; Wed, 15 Apr 2020 14:08:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0033.hostedemail.com [216.40.44.33]) by kanga.kvack.org (Postfix) with ESMTP id 8D6738E0001 for ; Wed, 15 Apr 2020 14:08:10 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 4B35F501F for ; Wed, 15 Apr 2020 18:08:10 +0000 (UTC) X-FDA: 76710873540.21.thumb47_d16f1a73914d X-HE-Tag: thumb47_d16f1a73914d X-Filterd-Recvd-Size: 5418 Received: from mail-oi1-f196.google.com (mail-oi1-f196.google.com [209.85.167.196]) by imf27.hostedemail.com (Postfix) with ESMTP for ; Wed, 15 Apr 2020 18:08:09 +0000 (UTC) Received: by mail-oi1-f196.google.com with SMTP id j16so14275982oih.10 for ; Wed, 15 Apr 2020 11:08:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Hj+w2b8MlzXiZplgu3jb4eTtjZmFrNnBBz27RkzElPo=; b=DzHggghtb9lsQ0Q5rBTqUiusLkpGRDErRwTCQaNB7sZoQf5TAYp0xUiSksirx/4JsR m7Apwvq72YGO9sUcFLt6/dyDGwdBmW2m2599IIObTzfKOD0FDWT6kbJ+ekPD6sXSG2xf AVP4hGdSZeM5wQ4RHQ5dfxMHkcYaboDyrJO1L8M3CiVBb4n12/jlgzn+zg4tuVPI8vZt eyDJmgSj0sCige7YQ6ntjy35dEfEh5FsmqVl0Miqj7owZ49B+kREg/rLwtz/zlj80g++ glY+vLySWV0GRC0blaC7+OKeq+DDghUZ4SYNDZlxXkMNvRyrbBHg10WQPxiR8JKOmgbF bJeA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Hj+w2b8MlzXiZplgu3jb4eTtjZmFrNnBBz27RkzElPo=; b=TeTCybwcTSgx27PqKQvN2oRkWqwm9sOWouVT8kwaZsMEKJW2+NhQxFGM3OJSNgcqQg JzWgEN722iqTp0QMedBsq63pxZW5aMU3Bn6K5tBPM3LR2LXoRApUhQ80B3puGhUjfKRa Z3PYU0yoJhKr+wlLgT3ro+9cvtUFRxSNFzYmnOXnDgq8snmpASuukSEk5H6voJInnVik 4Eg0uzirGEm9U8Hy5Ovis07p3dLgA2W4jHh2B7X/it0PCWfRRJiKvZbBF2gV5ZNKzmVG iTanHcbh8wWigf9dgxfHTrM6agmcUo4ljR5Vn/F1pP6N1BvZ1U+Ri9tHo7iinR+p2qVa 8KYQ== X-Gm-Message-State: AGi0Pub7loedSizXKZ6gSURsmCpwA3iLlIDSiPUOtEX1RqybYBtdlhml saI1EpWqz+ywvZXOBWPu0URU7JV3yXPLy1bO1gU/Hg== X-Google-Smtp-Source: APiQypLxNn+xKlz0LPCMbXE2SC11pDSOPtYcU6PNJY5ioAXG6B9257iqvNLz+mr50JDvbTk8i5s8S9BNWoZ5hgkfMHo= X-Received: by 2002:a05:6808:4e:: with SMTP id v14mr385130oic.70.1586974089086; Wed, 15 Apr 2020 11:08:09 -0700 (PDT) MIME-Version: 1.0 References: <202004151054.BD695840@keescook> In-Reply-To: <202004151054.BD695840@keescook> From: Marco Elver Date: Wed, 15 Apr 2020 20:07:57 +0200 Message-ID: Subject: Re: [PATCH] slub: Avoid redzone when choosing freepointer location To: Kees Cook Cc: Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Linux Memory Management List , LKML Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, 15 Apr 2020 at 19:55, Kees Cook wrote: > > Marco Elver reported system crashes when booting with "slub_debug=Z". > The freepointer location (s->offset) was not taking into account that > the "inuse" size that includes the redzone area should not be used by > the freelist pointer. Change the calculation to save the area of the > object that an inline freepointer may be written into. > > Reported-by: Marco Elver > Link: https://lore.kernel.org/linux-mm/20200415164726.GA234932@google.com > Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object") > Signed-off-by: Kees Cook Works for me, thank you! Tested-by: Marco Elver > --- > mm/slub.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 332d4b459a90..9bf44955c4f1 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -3533,6 +3533,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) > { > slab_flags_t flags = s->flags; > unsigned int size = s->object_size; > + unsigned int freepointer_area; > unsigned int order; > > /* > @@ -3541,6 +3542,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) > * the possible location of the free pointer. > */ > size = ALIGN(size, sizeof(void *)); > + /* > + * This is the area of the object where a freepointer can be > + * safely written. If redzoning adds more to the inuse size, we > + * can't use that portion for writing the freepointer, so > + * s->offset must be limited within this for the general case. > + */ > + freepointer_area = size; > > #ifdef CONFIG_SLUB_DEBUG > /* > @@ -3582,13 +3590,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) > */ > s->offset = size; > size += sizeof(void *); > - } else if (size > sizeof(void *)) { > + } else if (freepointer_area > sizeof(void *)) { > /* > * Store freelist pointer near middle of object to keep > * it away from the edges of the object to avoid small > * sized over/underflows from neighboring allocations. > */ > - s->offset = ALIGN(size / 2, sizeof(void *)); > + s->offset = ALIGN(freepointer_area / 2, sizeof(void *)); > } > > #ifdef CONFIG_SLUB_DEBUG > -- > 2.20.1 > > > -- > Kees Cook