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 566A9EB64DC for ; Tue, 11 Jul 2023 16:21:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D3EFC6B0072; Tue, 11 Jul 2023 12:21:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CEF3E6B0074; Tue, 11 Jul 2023 12:21:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BB7196B0075; Tue, 11 Jul 2023 12:21:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id A74496B0072 for ; Tue, 11 Jul 2023 12:21:43 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 4A0B9140313 for ; Tue, 11 Jul 2023 16:21:43 +0000 (UTC) X-FDA: 80999846886.14.2B38760 Received: from mail-pj1-f53.google.com (mail-pj1-f53.google.com [209.85.216.53]) by imf02.hostedemail.com (Postfix) with ESMTP id 97D178004F for ; Tue, 11 Jul 2023 16:21:38 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=gpWbxLEJ; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf02.hostedemail.com: domain of keescook@chromium.org designates 209.85.216.53 as permitted sender) smtp.mailfrom=keescook@chromium.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1689092498; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=FRd6MSnrDwuyQ7znWMqv6yCTnL1/DCJOC7bU8PD4YHA=; b=Xbh5jtcLw+cY0RfHrue8Wxzbh88FdZemoVkt9yrWzGNKwyLH+MKIAm12L1e2Ekf3yZvEqo yXuXoJkfqKpRk0XwlIOBVvUsuaE9kLiOI0/al9WuuE4Ee6AhN4VbNxLggAudz/RAUOlHH2 ILUdw81fu+gJXzivQ8YHIN9DV6ACprs= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=gpWbxLEJ; dmarc=pass (policy=none) header.from=chromium.org; spf=pass (imf02.hostedemail.com: domain of keescook@chromium.org designates 209.85.216.53 as permitted sender) smtp.mailfrom=keescook@chromium.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1689092498; a=rsa-sha256; cv=none; b=mLZJyuCwhsZRMMKwMPU0hGP5w8REnccnmX/zAiJGSIWvGBj46em+wsLVeo/GwebH5a+fNt LtvukmCZllI7G7exFaWnrWb/Nt9d1FKmLBMIhjY97kwPtHn/216JBOSMBsSvRs4sHohykO Sng9L/YE6P+ydhR+/YjkVQTR+9iFohs= Received: by mail-pj1-f53.google.com with SMTP id 98e67ed59e1d1-262e5e71978so3805069a91.1 for ; Tue, 11 Jul 2023 09:21:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1689092497; x=1691684497; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=FRd6MSnrDwuyQ7znWMqv6yCTnL1/DCJOC7bU8PD4YHA=; b=gpWbxLEJAvmtMRm+FhOebdn8dZhw/8ODnpNfzpB0MQM3pSJXTeWlGHA4rduGWhj+cX Ro43D8BRredizt+GPW75K5Q3Y+Dr3QH6caOSAfHsa+RWAxkbmzOtytqAsA0nIQKnhMse Bhf/WZN5knflEGP6D2uaxg9geafaqTw2FfFRY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689092497; x=1691684497; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=FRd6MSnrDwuyQ7znWMqv6yCTnL1/DCJOC7bU8PD4YHA=; b=H0gKcYAJ73DXnRqmSORxvGjQ0SEXaX0nST4HdVNnnYNXmsHvxwXBvzCdr98Fqm5HR6 O3G5CpK272VOs5FcXZ7Wy0K6WZIoyRa8Te+gdPQm16E63WgYjzTcSyr9Z3P1YQlg+3Cl dexFW1sYfg6B8hzqn+IHvYOByPrqfOlO0tNFwfDke/XhBvOWFdQsdLKnWk+VxbgrkXUN xpbeatY7KNZDnv0cSVMji83hjwDGcnLYKCT7ECO/rSBUDyfRD6/XDLvWQAP14/8J+jnZ CmJEikgaUnS83TVl0xvUZUg+ZW+C0sn46pWfK+KZJ8Xf3R5DgTN6Gi5w0QcGcYsvItXN E4+A== X-Gm-Message-State: ABy/qLYJMVmBhXs8YAAMUwmtXsGvl6u3zsGxfBgwWqbgpJPq+kjBzZxX vExwSaC+hD89PwxVE9lzVVS3NnSa9RWRsZ88/50= X-Google-Smtp-Source: APBJJlGmfygMjusEhLAateZabdJC+NgJo425Y8P55gtNUAQan1lVCm6MeEIhr+Us9T17E8ZvkbTgag== X-Received: by 2002:a17:90b:1d02:b0:263:114c:52fc with SMTP id on2-20020a17090b1d0200b00263114c52fcmr23830843pjb.12.1689092497290; Tue, 11 Jul 2023 09:21:37 -0700 (PDT) Received: from www.outflux.net (198-0-35-241-static.hfc.comcastbusiness.net. [198.0.35.241]) by smtp.gmail.com with ESMTPSA id dw16-20020a17090b095000b00260cce91d20sm2026175pjb.33.2023.07.11.09.21.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Jul 2023 09:21:36 -0700 (PDT) Date: Tue, 11 Jul 2023 09:21:36 -0700 From: Kees Cook To: Vlastimil Babka Cc: Christoph Lameter , David Rientjes , Pekka Enberg , Joonsoo Kim , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Roman Gushchin , linux-mm@kvack.org, patches@lists.linux.dev, linux-kernel@vger.kernel.org, Matteo Rizzo , Jann Horn , Andrey Konovalov , Marco Elver , Alexander Potapenko , kasan-dev@googlegroups.com, linux-hardening@vger.kernel.org Subject: Re: [PATCH 2/2] mm/slub: remove freelist_dereference() Message-ID: <202307110917.DEED145F0@keescook> References: <20230711134623.12695-3-vbabka@suse.cz> <20230711134623.12695-4-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230711134623.12695-4-vbabka@suse.cz> X-Rspam-User: X-Stat-Signature: u9ugyc8buo1rr3hk3gsmypwfzafizxzs X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 97D178004F X-HE-Tag: 1689092498-711050 X-HE-Meta: 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 dvKBOGgX 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 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 Tue, Jul 11, 2023 at 03:46:25PM +0200, Vlastimil Babka wrote: > freelist_dereference() is a one-liner only used from get_freepointer(). > Remove it and make get_freepointer() call freelist_ptr_decode() > directly to make the code easier to follow. > > Signed-off-by: Vlastimil Babka > --- > mm/slub.c | 16 ++++++---------- > 1 file changed, 6 insertions(+), 10 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 07edad305512..c4556a5dab4b 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -397,18 +397,14 @@ static inline void *freelist_ptr_decode(const struct kmem_cache *s, > return decoded; > } > > -/* Returns the freelist pointer recorded at location ptr_addr. */ > -static inline void *freelist_dereference(const struct kmem_cache *s, > - void *ptr_addr) > -{ > - return freelist_ptr_decode(s, *(freeptr_t *)(ptr_addr), > - (unsigned long)ptr_addr); > -} > - > static inline void *get_freepointer(struct kmem_cache *s, void *object) > { > - object = kasan_reset_tag(object); > - return freelist_dereference(s, (freeptr_t *)(object + s->offset)); > + unsigned long ptr_addr; > + freeptr_t p; > + > + ptr_addr = ((unsigned long)kasan_reset_tag(object)) + s->offset; > + p = *(freeptr_t *)(ptr_addr); > + return freelist_ptr_decode(s, p, ptr_addr); > } > > #ifndef CONFIG_SLUB_TINY > -- > 2.41.0 > I like reducing the complexity here, but I find dropping the "object" reassignment makes this a bit harder to read. What about: object = kasan_reset_tag(object); unsigned long ptr_addr = (unsigned long)object + s->offset; freeptr_t p = *(freeptr_t *)(ptr_addr); return freelist_ptr_decode(s, p, ptr_addr); ? They're the same result, so either way: Acked-by: Kees Cook -- Kees Cook