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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 C1F5CC43461 for ; Wed, 16 Sep 2020 00:28:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8AFE220663 for ; Wed, 16 Sep 2020 00:28:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726790AbgIPA1g (ORCPT ); Tue, 15 Sep 2020 20:27:36 -0400 Received: from verein.lst.de ([213.95.11.211]:47847 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726789AbgIOOHY (ORCPT ); Tue, 15 Sep 2020 10:07:24 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id C892268AFE; Tue, 15 Sep 2020 16:07:19 +0200 (CEST) Date: Tue, 15 Sep 2020 16:07:19 +0200 From: Christoph Hellwig To: Thomas Tai Cc: konrad.wilk@oracle.com, m.szyprowski@samsung.com, hch@lst.de, robin.murphy@arm.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dma-direct: Fix potential NULL pointer dereference Message-ID: <20200915140719.GA14831@lst.de> References: <1600178594-22801-1-git-send-email-thomas.tai@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1600178594-22801-1-git-send-email-thomas.tai@oracle.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 15, 2020 at 08:03:14AM -0600, Thomas Tai wrote: > When booting the kernel v5.9-rc4 on a VM, the kernel would panic when > printing a warning message in swiotlb_map(). It is because dev->dma_mask > can potentially be a null pointer. Using the dma_get_mask() macro can > avoid the NULL pointer dereference. dma_mask must not be zero. This means drm is calling DMA API functions on something weird. This needs to be fixed in the caller.