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=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 E2EA0CA9ECE for ; Thu, 31 Oct 2019 17:22:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AB27520873 for ; Thu, 31 Oct 2019 17:22:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB27520873 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 236186B000D; Thu, 31 Oct 2019 13:22:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1E6CC6B000E; Thu, 31 Oct 2019 13:22:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0D5436B0010; Thu, 31 Oct 2019 13:22:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0165.hostedemail.com [216.40.44.165]) by kanga.kvack.org (Postfix) with ESMTP id DEBCB6B000D for ; Thu, 31 Oct 2019 13:22:53 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id 5B2E78249980 for ; Thu, 31 Oct 2019 17:22:53 +0000 (UTC) X-FDA: 76104749826.14.can48_535965e2b804a X-HE-Tag: can48_535965e2b804a X-Filterd-Recvd-Size: 5541 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Thu, 31 Oct 2019 17:22:52 +0000 (UTC) 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 Cc: "linux-mm@kvack.org" , Andy Lutomirski , Ard Biesheuvel , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Dave Hansen , Ingo Molnar , James Morse , =?iso-8859-1?B?Suly9G1l?= Glisse , Peter Zijlstra , Thomas Gleixner , Will Deacon , "x86@kernel.org" , "H. Peter Anvin" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Mark Rutland , "Liang, Kan" , Andrew Morton , Zong Li , "lkp@lists.01.org" , "ltp@lists.linux.it" 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191031151510.GA16405@xsang-OptiPlex-9020> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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