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=-10.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 C8DDCCA9ECB for ; Thu, 31 Oct 2019 17:23:03 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9D2202086D for ; Thu, 31 Oct 2019 17:23:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="pqV1KT49" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9D2202086D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=fYx8jFbFIBNUqYW7MrBp5rc6hapdEiVWfTzOVJxoapA=; b=pqV1KT4911qlfv yjAgAT/1LRHZC05TrtaBGvLUlABYnBAtjISeraO+bvWJXszlnHE8Sx26lF+Fu10iUhYE5VvCGBNaT ddmChlzpsb7WXW3A8GgrZnfyqITM6yug1fn++9Jz+8WP3iSMNGkJ2HZYRgTwT25/H+FE2As+91/TJ X4dn6+kHlH7ZB5/2yiBRIyumoX6t3uYlmWbHPwUA7bXFdOq6DresECJfM5MVQzbMKTT0poyd2+svL 0Qb5E6mVLT5tRfm0RMSvmPiUHXndHKxYoKe9s3999TZz8tX943J1nQ//UbbU7PYjK+/UepYdxMLbk mS3o5yerVkBvPHg2attg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1iQE9v-0002Y1-Ry; Thu, 31 Oct 2019 17:22:55 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1iQE9t-0002XB-0n for linux-arm-kernel@lists.infradead.org; Thu, 31 Oct 2019 17:22:54 +0000 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 C50F11FB; Thu, 31 Oct 2019 10:22:51 -0700 (PDT) Received: from arm.com (e112269-lin.cambridge.arm.com [10.1.194.43]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DFE213F6C4; Thu, 31 Oct 2019 10:22:48 -0700 (PDT) Date: Thu, 31 Oct 2019 17:22:43 +0000 From: Steven Price To: lkp report check Subject: Re: [mm] 9343f6818b: BUG:kernel_NULL_pointer_dereference,address Message-ID: <20191031172241.GA54073@arm.com> References: <20191028135910.33253-13-steven.price@arm.com> <20191031151510.GA16405@xsang-OptiPlex-9020> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20191031151510.GA16405@xsang-OptiPlex-9020> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191031_102253_152220_AA82C1FF X-CRM114-Status: GOOD ( 17.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Peter Zijlstra , Catalin Marinas , Dave Hansen , "linux-mm@kvack.org" , Zong Li , "H. Peter Anvin" , Will Deacon , "Liang, Kan" , "x86@kernel.org" , Ingo Molnar , "ltp@lists.linux.it" , Arnd Bergmann , "lkp@lists.01.org" , =?iso-8859-1?B?Suly9G1l?= Glisse , Borislav Petkov , Andy Lutomirski , Thomas Gleixner , "linux-arm-kernel@lists.infradead.org" , Ard Biesheuvel , "linux-kernel@vger.kernel.org" , James Morse , Andrew Morton Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 31, 2019 at 03:15:10PM +0000, kernel test robot wrote: > FYI, we noticed the following commit (built with gcc-7): > > commit: 9343f6818bb98cf0c982bfff6ed89b2c7176bcf9 ("[PATCH v14 12/22] mm: pagewalk: Allow walking without vma") > url: https://github.com/0day-ci/linux/commits/Steven-Price/Generic-page-walk-and-ptdump/20191030-085205 > [...] > > [ 36.010874] BUG: kernel NULL pointer dereference, address: 0000000000000053 > [ 36.012644] #PF: supervisor read access in kernel mode > [ 36.014074] #PF: error_code(0x0000) - not-present page > [ 36.015481] PGD 0 P4D 0 > [ 36.016433] Oops: 0000 [#1] SMP PTI > [ 36.017561] CPU: 1 PID: 2376 Comm: mmap12 Not tainted 5.4.0-rc5-00046-g9343f6818bb98 #1 > [ 36.019340] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 > [ 36.021250] RIP: 0010:pagemap_pmd_range+0x5ae/0x7b0 So it looks like this has broken /proc//pagemap because we can now call the callbacks with a NULL vma if the region passed into walk_page_range is (partially) outside the VMA range. Somehow, in this situation, there is a region which has a PMD entry but no corresponding VMA. So the pmd_entry callback is called but with walk->vma==NULL. The options for fixing this seem to be: a) Make the pagemap callback robust against a PMD entry without a VMA. For example treating it as a hole (as it would have been before this patch): ---8<--- diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 9442631fd4af..b6d819c4bbb2 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1369,6 +1369,9 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end, pte_t *pte, *orig_pte; int err = 0; + if (!vma) + return pagemap_pte_hole(addr, end, walk); + #ifdef CONFIG_TRANSPARENT_HUGEPAGE ptl = pmd_trans_huge_lock(pmdp, vma); if (ptl) { ---8<--- b) Provide a flag (or another function) for walk_page_range() which restores the previous behaviour. Only those users that want to walk ranges without VMAs would then need to deal with NULL-vma returns. ---8<--- diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h index 12004b097eae..519258e8fffa 100644 --- a/include/linux/pagewalk.h +++ b/include/linux/pagewalk.h @@ -61,6 +61,7 @@ struct mm_walk { const struct mm_walk_ops *ops; struct mm_struct *mm; struct vm_area_struct *vma; + bool ignore_vma; void *private; }; diff --git a/mm/pagewalk.c b/mm/pagewalk.c index 4139e9163aee..f2fccbc3cba8 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -38,7 +38,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, do { again: next = pmd_addr_end(addr, end); - if (pmd_none(*pmd)) { + if (pmd_none(*pmd) || (!walk->vma && walk->ignore_vma)) { if (ops->pte_hole) err = ops->pte_hole(addr, next, walk); if (err) @@ -89,7 +89,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, do { again: next = pud_addr_end(addr, end); - if (pud_none(*pud)) { + if (pud_none(*pud) || (!walk->vma && !walk->ignore_vma)) { if (ops->pte_hole) err = ops->pte_hole(addr, next, walk); if (err) ---8<--- I'm currently inclined towards the latter because I don't want to have to try to audit all existing users in case there's anything similar lurking in another user of walk_page_range(). Steve _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel