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Tue, 15 Sep 2020 14:40:44 +0000 Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id 08FEeckQ019070; Tue, 15 Sep 2020 14:40:38 GMT Received: from [10.39.253.102] (/10.39.253.102) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 15 Sep 2020 14:40:38 +0000 Subject: Re: [PATCH] dma-direct: Fix potential NULL pointer dereference To: Christoph Hellwig References: <1600178594-22801-1-git-send-email-thomas.tai@oracle.com> <20200915140719.GA14831@lst.de> <20200915142624.GA16005@lst.de> From: Thomas Tai Message-ID: Date: Tue, 15 Sep 2020 10:40:39 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200915142624.GA16005@lst.de> Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9744 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 spamscore=0 adultscore=0 suspectscore=0 mlxscore=0 bulkscore=0 mlxlogscore=999 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009150123 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9744 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 spamscore=0 lowpriorityscore=0 malwarescore=0 mlxscore=0 bulkscore=0 suspectscore=0 clxscore=1015 mlxlogscore=999 adultscore=0 priorityscore=1501 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2009150123 Cc: iommu@lists.linux-foundation.org, robin.murphy@arm.com, linux-kernel@vger.kernel.org, konrad.wilk@oracle.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 2020-09-15 10:26 a.m., Christoph Hellwig wrote: > 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; > - I am concerned that some drivers may rely on this NULL checking. Would you think we can keep this checking and use the following WARN_ON_ONCE()? > 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) > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu