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=-8.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 DB756C43461 for ; Wed, 16 Sep 2020 00:10:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A74E220738 for ; Wed, 16 Sep 2020 00:10:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727376AbgIPAKe (ORCPT ); Tue, 15 Sep 2020 20:10:34 -0400 Received: from verein.lst.de ([213.95.11.211]:47944 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726395AbgIOO0u (ORCPT ); Tue, 15 Sep 2020 10:26:50 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 9107768BFE; Tue, 15 Sep 2020 16:26:25 +0200 (CEST) Date: Tue, 15 Sep 2020 16:26:24 +0200 From: Christoph Hellwig To: Thomas Tai Cc: Christoph Hellwig , konrad.wilk@oracle.com, m.szyprowski@samsung.com, 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: <20200915142624.GA16005@lst.de> References: <1600178594-22801-1-git-send-email-thomas.tai@oracle.com> <20200915140719.GA14831@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 10:11:51AM -0400, Thomas Tai wrote: > > > On 2020-09-15 10:07 a.m., Christoph Hellwig wrote: >> 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. >> > > Thanks, Christoph for your comment. The caller already fixed the null > pointer in the latest v5.9-rc5. I am thinking that if we had used the > dma_get_mask(), the kernel couldn't panic and could properly print out the > warning message. If we want to solve this something like this patch is probably the right way: diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h index 6e87225600ae35..064870844f06c1 100644 --- a/include/linux/dma-direct.h +++ b/include/linux/dma-direct.h @@ -62,9 +62,6 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size, { dma_addr_t end = addr + size - 1; - if (!dev->dma_mask) - return false; - if (is_ram && !IS_ENABLED(CONFIG_ARCH_DMA_ADDR_T_64BIT) && min(addr, end) < phys_to_dma(dev, PFN_PHYS(min_low_pfn))) return false; diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c index 0d129421e75fc8..2b01d8f7baf160 100644 --- a/kernel/dma/mapping.c +++ b/kernel/dma/mapping.c @@ -144,6 +144,10 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page, dma_addr_t addr; BUG_ON(!valid_dma_direction(dir)); + + if (WARN_ON_ONCE(!dev->dma_mask)) + return DMA_MAPPING_ERROR; + if (dma_map_direct(dev, ops)) addr = dma_direct_map_page(dev, page, offset, size, dir, attrs); else @@ -179,6 +183,10 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents, int ents; BUG_ON(!valid_dma_direction(dir)); + + if (WARN_ON_ONCE(!dev->dma_mask)) + return 0; + if (dma_map_direct(dev, ops)) ents = dma_direct_map_sg(dev, sg, nents, dir, attrs); else @@ -217,6 +225,9 @@ dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr, if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr)))) return DMA_MAPPING_ERROR; + if (WARN_ON_ONCE(!dev->dma_mask)) + return DMA_MAPPING_ERROR; + if (dma_map_direct(dev, ops)) addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs); else if (ops->map_resource)