From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0EEE674416 for ; Thu, 25 Apr 2024 08:37:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714034227; cv=none; b=gr7w8LG7H2byiSMitS6qwbleSaVueVN0LW6zlwXc8l3Eu2vYtN9VAyjKJjPEIS4ZeCrc5Wp6shBV90htsOOExqNWbLpIhff4LZtz8G0avynaQqzDy6jKb5vVbyUoHhAaSlO+Tvs4J8JMqtZ+rxIuiO1K57QLFUo0TlLVrandJK8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714034227; c=relaxed/simple; bh=JizmCAqR2AD7zZZ2PmQ4NLKtsj6pjsjNTKBWvGZfPI0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=S8ZUoZxNejlKPPC6Rliw4EeC7sr8VBtyM6yq53+jZaOCfkkdygzsfiY8vTl2UvrC7PnkI3KiTQwvYtfTW70DzmRjL4mIscz46EMfQZuvUuZ+KW9w25j2pvdrEwrAtrLjFUDZ7637hIXHvM8/2AYzm8lE62Jb2SgQ5LrbGakzo24= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=twvjcBTS; arc=none smtp.client-ip=95.215.58.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="twvjcBTS" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1714034221; 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=E8Dv8ja4cI4A7RuODPGz/1zq0mfPiA4Ztqb9IZnHmtE=; b=twvjcBTST93NpvA3XgZgY6DoXLHBuOSyuy7O4G4p72MyO+AU4mK+Q4ipfbgJaTOxqwi+wB As0Sh3j+b8vDzwF2a3828/eq19a5mm3hIlNBT8qT1hI8c1kzyI5lZ/QPHD81rOQ6h1iowR DjdeZG/S09zYpPqYB6KVqVxu7dPBLjQ= Date: Thu, 25 Apr 2024 16:36:53 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: 7bit X-Migadu-Flow: FLOW_OUT 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? 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