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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1C631C00144 for ; Mon, 1 Aug 2022 18:48:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233181AbiHASsE (ORCPT ); Mon, 1 Aug 2022 14:48:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41470 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231797AbiHASsD (ORCPT ); Mon, 1 Aug 2022 14:48:03 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6AE8522BC5 for ; Mon, 1 Aug 2022 11:48:01 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CAE8F139F; Mon, 1 Aug 2022 11:48:01 -0700 (PDT) Received: from [10.57.10.23] (unknown [10.57.10.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1EFDF3F67D; Mon, 1 Aug 2022 11:47:58 -0700 (PDT) Message-ID: <15735fab-e53d-e95d-84f8-ae2e435dbb78@arm.com> Date: Mon, 1 Aug 2022 19:47:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH] dma-debug: Fix overflow issue in bucket_find_contain Content-Language: en-GB To: yf.wang@mediatek.com, Christoph Hellwig , Marek Szyprowski , Matthias Brugger , "open list:DMA MAPPING HELPERS" , open list , "moderated list:ARM/Mediatek SoC support" , "moderated list:ARM/Mediatek SoC support" Cc: wsd_upstream@mediatek.com, Libo Kang , Ning Li , Yong Wu , Miles Chen , jianjiao zeng References: <20220730114146.32669-1-yf.wang@mediatek.com> From: Robin Murphy In-Reply-To: <20220730114146.32669-1-yf.wang@mediatek.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022-07-30 12:41, yf.wang@mediatek.com wrote: > From: Yunfei Wang > > There are two issue: > 1. If max_rang is set to 0xFFFF_FFFF, and __hash_bucket_find always > returns NULL, the rang will be accumulated. When rang is accumulated > to 0xFFFF_E000, after executing rang += (1 << HASH_FN_SHIFT) again, > rang will overflow to 0, making it impossible to exit the while loop. > 2. dev_addr reduce maybe overflow. > > So, add range and dev_addr check to avoid overflow. > > Signed-off-by: jianjiao zeng > Signed-off-by: Yunfei Wang > --- > kernel/dma/debug.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c > index ad731f7858c9..9d7d54cd4c63 100644 > --- a/kernel/dma/debug.c > +++ b/kernel/dma/debug.c > @@ -352,6 +352,7 @@ static struct dma_debug_entry *bucket_find_contain(struct hash_bucket **bucket, > > unsigned int max_range = dma_get_max_seg_size(ref->dev); > struct dma_debug_entry *entry, index = *ref; > + unsigned int shift = (1 << HASH_FN_SHIFT); > unsigned int range = 0; > > while (range <= max_range) { > @@ -360,12 +361,15 @@ static struct dma_debug_entry *bucket_find_contain(struct hash_bucket **bucket, > if (entry) > return entry; > > + if (max_range - range < shift || index.dev_addr < shift) > + return NULL; This seems a bit clunky since the first condition here effectively makes the loop condition redundant. FWIW I found the whole "range" business here rather hard to make sense of - personally I'd calculate a lower bound for the address then just iterate down to that, but maybe that's just me :/ Otherwise, at the very least we should be capping max_range so that the loop doesn't go beyond HASH_SIZE iterations and pointlessly search the same buckets more than once - it's stupid to even *get* to the point of having to worry about that overflowing. Whether we really care about dev_addr underflow is then another matter. Really it would seem even more logical to make this a lower-level function that can walk round the dma_entry_hash array directly and not have to monkey about with the fake "index" entry at all, but cleaning up the almost-unnecessary amount of internal abstractions here is maybe more work than it's worth at this point. Robin. > + > /* > * Nothing found, go back a hash bucket > */ > put_hash_bucket(*bucket, *flags); > - range += (1 << HASH_FN_SHIFT); > - index.dev_addr -= (1 << HASH_FN_SHIFT); > + range += shift; > + index.dev_addr -= shift; > *bucket = get_hash_bucket(&index, flags); > } >