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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,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 666C1C433E2 for ; Tue, 15 Sep 2020 15:08:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F2C912067C for ; Tue, 15 Sep 2020 15:08:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="Vt67dayv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727424AbgIOPHx (ORCPT ); Tue, 15 Sep 2020 11:07:53 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:59620 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727025AbgIOOlb (ORCPT ); Tue, 15 Sep 2020 10:41:31 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 08FEduQ2150785; Tue, 15 Sep 2020 14:40:45 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2020-01-29; bh=ob0tiNJJ2VTB74z1m5YoBvbdwfodTrserhVba6hRRVA=; b=Vt67dayvJ1CvcEjVXjDDNI5aiebMMgRTZ+Dn0mmB0GYmPHxMq86FGGwhHOdq33uwb3Ip WQ48SLXqtcmtSGzjHt74Qs/fh1b3UtsCi8Hae1P4BQAIBhfThupREHYmsEpkizByfySo cHv3PEg+CPF3K4H231lfBoH9VFOROPwVR9mzVi5sTYXfCHjDMPmmd234Sy9e5CyWUUwx tptRdXw381UFl/eUZeO6bKEqZI4KSuwYeocSLitWAwX9iCjdoHn8/+W8h0K2+lPZojCT U6a1jIQHhHsdB1qlJ6LiI3D6M7wWYEJP0R7d+0n7TeK0Oc5xSzuE0obnSTxiTeJRBWh9 qg== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2130.oracle.com with ESMTP id 33gnrqwg95-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 15 Sep 2020 14:40:45 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 08FEeiYi095980; Tue, 15 Sep 2020 14:40:45 GMT Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userp3030.oracle.com with ESMTP id 33h88ye624-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); 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 Cc: konrad.wilk@oracle.com, m.szyprowski@samsung.com, robin.murphy@arm.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org 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-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) >