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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id EC2CDC19F4E for ; Thu, 25 Apr 2024 15:15:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 79D9A6B009D; Thu, 25 Apr 2024 11:15:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 74D1B6B009F; Thu, 25 Apr 2024 11:15:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5C8BA6B00A0; Thu, 25 Apr 2024 11:15:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 3627D6B009D for ; Thu, 25 Apr 2024 11:15:20 -0400 (EDT) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id CD5591612B9 for ; Thu, 25 Apr 2024 15:15:19 +0000 (UTC) X-FDA: 82048402758.27.86F0243 Received: from out-173.mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) by imf07.hostedemail.com (Postfix) with ESMTP id 4D84B40022 for ; Thu, 25 Apr 2024 15:15:16 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=CI1gmBoJ; spf=pass (imf07.hostedemail.com: domain of chengming.zhou@linux.dev designates 95.215.58.173 as permitted sender) smtp.mailfrom=chengming.zhou@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1714058118; h=from:from:sender: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:dkim-signature; bh=ZyCEiDB794H0D6y6L88y3ywwU1X/3LX93YpO6CxtZCE=; b=pepma3ddP7ah4nXGeO8m3MrzpdFe3FiPVduZF5K0BBxwZrWSNivnDoxuHwSUUdj6tQ+h2e ggZrruYVAyQiiux8Kt97deEbZx+XdnnOn0YTuajP0qS537+Lg8nZuUiisB9aJw5Ayrr6bu yvv9qgDwHtQWC7F0i0Y7wLd2FsofBfo= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1714058118; a=rsa-sha256; cv=none; b=s3HwapIJBp+tpVxLeao3pQlIIEKYASbmO0CW1mm0gKlhF0sL8LhDY1nZwLgJdWsEwvhQfN iiHCNmgMe5VBqstZpFzbc8TWRPe6Vx1GATgK+ZVvJKgtLUQptxFLGyfcxnSUqik0pZamep a6Eq7QNqWL6DSbiMzP+L/qImwt+SLno= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=CI1gmBoJ; spf=pass (imf07.hostedemail.com: domain of chengming.zhou@linux.dev designates 95.215.58.173 as permitted sender) smtp.mailfrom=chengming.zhou@linux.dev; dmarc=pass (policy=none) header.from=linux.dev Message-ID: <5c34b253-b476-494a-96c9-fe3c95b9b74d@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1714058114; 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=ZyCEiDB794H0D6y6L88y3ywwU1X/3LX93YpO6CxtZCE=; b=CI1gmBoJCJOchdIwbeCtHlv2TeilpTqx6HUFllreyv5TaDQSTi+lbYa52P3VU4EYR/Z14I dDurtOEmT4AWAdWa8tbmbIOeh5VIr8vN8b+TlctZFFO8QLX0g/kavySs4ktjKupVj5mRz/ erJA9+yE9FPyfRtVFJLD3lSXeh5HFbA= Date: Thu, 25 Apr 2024 23:14:59 +0800 MIME-Version: 1.0 Subject: Re: [PATCH] slub: Fixes freepointer encoding for single free To: Nicolas Bouchinet , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com References: Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Chengming Zhou In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 4D84B40022 X-Rspam-User: X-Stat-Signature: 9ata1s1q9dn4zwifiqo6q1zjdbjgfzgh X-HE-Tag: 1714058116-351128 X-HE-Meta: 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 uMwBVxU9 q+JZr4cuX9SsoEkMH+uhsCuskXTeL0hCvsXXSsJOwMHaPCL7YwQ1BGE6+VakMgFuIxd1tvnFi34ta7GzjXVP+bZX9pUxPiw1DaduSSB7xAKL6/9PAGigoYKhtey7o5BpKqiNWkqATYi/1QkpYpULKcCkueTuMHYJog9yWplkMMkVSVT1OyyFHyklZq3U3v7Wrr4Tt 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: List-Subscribe: List-Unsubscribe: On 2024/4/25 23:02, Nicolas Bouchinet wrote: > Hy, > > First of all, thanks a lot for your time. > > On 4/25/24 10:36, Chengming Zhou wrote: >> On 2024/4/24 20:47, Nicolas Bouchinet wrote: >>> From: Nicolas Bouchinet >>> >>> Commit 284f17ac13fe ("mm/slub: handle bulk and single object freeing >>> separately") splits single and bulk object freeing in two functions >>> slab_free() and slab_free_bulk() which leads slab_free() to call >>> slab_free_hook() directly instead of slab_free_freelist_hook(). >> Right. >> >>> If `init_on_free` is set, slab_free_hook() zeroes the object. >>> Afterward, if `slub_debug=F` and `CONFIG_SLAB_FREELIST_HARDENED` are >>> set, the do_slab_free() slowpath executes freelist consistency >>> checks and try to decode a zeroed freepointer which leads to a >>> "Freepointer corrupt" detection in check_object(). >> IIUC, the "freepointer" can be checked on the free path only when >> it's outside the object memory. Here slab_free_hook() zeroed the >> freepointer and caused the problem. >> >> But why we should zero the memory outside the object_size? It seems >> more reasonable to only zero the object_size when init_on_free is set? > > The original purpose was to avoid leaking information through the object and its metadata / tracking information as described in init_on_free initial Commit 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options"). > > I have to admit I didn't read the entire lore about the original patchset yet, though it could be interesting to know a bit more the threat models, specifically regarding the object metadata init. Thank you for the reference! I also don't get why it needs to zero the metadata and tracking information. > > The patch could also be optimized a bit by restricting set_freepointer() call to the `CONFIG_SLAB_FREELIST_HARDENED` option value. > Yeah. Maybe memcg_alloc_abort_single() needs this too. Thanks. > Thanks again, Nicolas > >> >> Thanks. >> >>> Object's freepointer thus needs to be properly set using >>> set_freepointer() after init_on_free. >>> >>> To reproduce, set `slub_debug=FU init_on_free=1 log_level=7` on the >>> command line of a kernel build with `CONFIG_SLAB_FREELIST_HARDENED=y`. >>> >>> dmesg sample log: >>> [   10.708715] ============================================================================= >>> [   10.710323] BUG kmalloc-rnd-05-32 (Tainted: G    B           T ): Freepointer corrupt >>> [   10.712695] ----------------------------------------------------------------------------- >>> [   10.712695] >>> [   10.712695] Slab 0xffffd8bdc400d580 objects=32 used=4 fp=0xffff9d9a80356f80 flags=0x200000000000a00(workingset|slab|node=0|zone=2) >>> [   10.716698] Object 0xffff9d9a80356600 @offset=1536 fp=0x7ee4f480ce0ecd7c >>> [   10.716698] >>> [   10.716698] Bytes b4 ffff9d9a803565f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................ >>> [   10.720703] Object   ffff9d9a80356600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................ >>> [   10.720703] Object   ffff9d9a80356610: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................ >>> [   10.724696] Padding  ffff9d9a8035666c: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................ >>> [   10.724696] Padding  ffff9d9a8035667c: 00 00 00 00                                      .... >>> [   10.724696] FIX kmalloc-rnd-05-32: Object at 0xffff9d9a80356600 not freed >>> >>> Signed-off-by: Nicolas Bouchinet >>> --- >>>   mm/slub.c | 8 +++++++- >>>   1 file changed, 7 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/slub.c b/mm/slub.c >>> index 3aa12b9b323d9..71dbff9ad8f17 100644 >>> --- a/mm/slub.c >>> +++ b/mm/slub.c >>> @@ -4342,10 +4342,16 @@ static __fastpath_inline >>>   void slab_free(struct kmem_cache *s, struct slab *slab, void *object, >>>              unsigned long addr) >>>   { >>> +    bool init = false; >>> + >>>       memcg_slab_free_hook(s, slab, &object, 1); >>> +    init = slab_want_init_on_free(s); >>>   -    if (likely(slab_free_hook(s, object, slab_want_init_on_free(s)))) >>> +    if (likely(slab_free_hook(s, object, init))) { >>> +        if (init) >>> +            set_freepointer(s, object, NULL); >>>           do_slab_free(s, slab, object, object, 1, addr); >>> +    } >>>   } >>>     static __fastpath_inline