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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 CF40FC433E0 for ; Mon, 18 May 2020 18:56:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 99C23207F5 for ; Mon, 18 May 2020 18:56:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589828190; bh=hDMgtnIxdRMx+igFYjzxKFmJlSiLPrW678U2lAXrdCk=; h=Date:From:To:Cc:Subject:List-ID:From; b=npsSvzoH+bnU8Hz3pIfKPDuUENfXG6bj9qGKrbMTpJbe2fxb7nA9MdWrWr8Aeknb7 rpJJLyr1VKPLi8FLPSYFaahsDGWshhU09+YX/bAMzXYrMko6p1KXUAADqMVDgM+Lnb Jgxhv6gha8b78S0H/3W5WJCcxEjWwY9YNMRk+FFA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729490AbgERS4a (ORCPT ); Mon, 18 May 2020 14:56:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:59562 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728436AbgERS43 (ORCPT ); Mon, 18 May 2020 14:56:29 -0400 Received: from embeddedor (unknown [189.207.59.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0B3B9207C4; Mon, 18 May 2020 18:56:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589828188; bh=hDMgtnIxdRMx+igFYjzxKFmJlSiLPrW678U2lAXrdCk=; h=Date:From:To:Cc:Subject:From; b=wLTG3i8+7pPhsNcmxh/tfuPi0KAiN9+rNwYF1Ar/qzZCPDuddh4MBl2oObDKZ0uIB PkpBpv8RvJ9RMkacE5cZE0RVwwI4UYXgO5EPdBz3Ue8k3HCinQz8WFUi2+646ARBCo 9UDy8HCyIeRIaig29rKCy3h4f+scZmjVqeq+mI3c= Date: Mon, 18 May 2020 14:01:14 -0500 From: "Gustavo A. R. Silva" To: Darren Hart , Andy Shevchenko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "x86@kernel.org H. Peter Anvin" Cc: platform-driver-x86@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" , Kees Cook Subject: [PATCH] x86/uv/time: Replace one-element array and save heap space Message-ID: <20200518190114.GA7757@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The current codebase makes use of one-element arrays in the following form: struct something { int length; u8 data[1]; }; struct something *instance; instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); instance->length = size; memcpy(instance->data, source, size); but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. So, replace the one-element array with a flexible-array member. Also, make use of the new struct_size() helper to properly calculate the total size needed to allocate dynamic memory for struct uv_rtc_timer_head. Notice that, due to the use of a one-element array, space for an extra struct cpu: struct { int lcpu; /* systemwide logical cpu number */ u64 expires; /* next timer expiration for this cpu */ } cpu[1] was being allocated at the moment of applying the sizeof operator to struct uv_rtc_timer_head in the call to kmalloc_node() at line 159: 159 head = kmalloc_node(sizeof(struct uv_rtc_timer_head) + 160 (uv_blade_nr_possible_cpus(bid) * 161 2 * sizeof(u64)), 162 GFP_KERNEL, nid); but that extra cpu[] was never actually being accessed due to the following piece of code at line 168: 168 head->ncpus = uv_blade_nr_possible_cpus(bid); and the piece of code at line 187: 187 for (c = 0; c < head->ncpus; c++) { 188 u64 exp = head->cpu[c].expires; 189 if (exp < lowest) { 190 bcpu = c; 191 lowest = exp; 192 } 193 } so heap space was being wasted. Another thing important to notice is that through the use of the struct_size() helper, code at line 161: 161 2 * sizeof(u64)), is changed to now be the actual size of struct cpu; see sizeof(*(p)->member) at include/linux/overflow.h:314: 314 #define struct_size(p, member, n) \ 315 __ab_c_size(n, \ 316 sizeof(*(p)->member) + __must_be_array((p)->member),\ 317 sizeof(*(p))) As a side note, the original developer could have implemented code at line 161: 2 * sizeof(64) as follows: sizeof(*head->cpu) This issue has been out there since 2009. This issue was found with the help of Coccinelle and fixed _manually_. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva --- arch/x86/platform/uv/uv_time.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/arch/x86/platform/uv/uv_time.c b/arch/x86/platform/uv/uv_time.c index 7af31b245636..993a8ae6fdfb 100644 --- a/arch/x86/platform/uv/uv_time.c +++ b/arch/x86/platform/uv/uv_time.c @@ -52,7 +52,7 @@ struct uv_rtc_timer_head { struct { int lcpu; /* systemwide logical cpu number */ u64 expires; /* next timer expiration for this cpu */ - } cpu[1]; + } cpu[]; }; /* @@ -156,9 +156,8 @@ static __init int uv_rtc_allocate_timers(void) struct uv_rtc_timer_head *head = blade_info[bid]; if (!head) { - head = kmalloc_node(sizeof(struct uv_rtc_timer_head) + - (uv_blade_nr_possible_cpus(bid) * - 2 * sizeof(u64)), + head = kmalloc_node(struct_size(head, cpu, + uv_blade_nr_possible_cpus(bid)), GFP_KERNEL, nid); if (!head) { uv_rtc_deallocate_timers(); -- 2.26.2