From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759324Ab3BMMOy (ORCPT ); Wed, 13 Feb 2013 07:14:54 -0500 Received: from terminus.zytor.com ([198.137.202.10]:36626 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754310Ab3BMMOx (ORCPT ); Wed, 13 Feb 2013 07:14:53 -0500 Date: Wed, 13 Feb 2013 04:12:03 -0800 From: tip-bot for Mel Gorman Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, hannes@cmpxchg.org, riel@redhat.coM, mgorman@suse.de, tglx@linutronix.de, mhocko@suse.cz Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, riel@redhat.coM, mgorman@suse.de, hannes@cmpxchg.org, tglx@linutronix.de, mhocko@suse.cz In-Reply-To: <20130211145236.GX21389@suse.de> References: <20130211145236.GX21389@suse.de> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/mm: Check if PUD is large when validating a kernel address Git-Commit-ID: 0ee364eb316348ddf3e0dfcd986f5f13f528f821 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (terminus.zytor.com [127.0.0.1]); Wed, 13 Feb 2013 04:12:10 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 0ee364eb316348ddf3e0dfcd986f5f13f528f821 Gitweb: http://git.kernel.org/tip/0ee364eb316348ddf3e0dfcd986f5f13f528f821 Author: Mel Gorman AuthorDate: Mon, 11 Feb 2013 14:52:36 +0000 Committer: Ingo Molnar CommitDate: Wed, 13 Feb 2013 10:02:55 +0100 x86/mm: Check if PUD is large when validating a kernel address A user reported the following oops when a backup process reads /proc/kcore: BUG: unable to handle kernel paging request at ffffbb00ff33b000 IP: [] kern_addr_valid+0xbe/0x110 [...] Call Trace: [] read_kcore+0x17a/0x370 [] proc_reg_read+0x77/0xc0 [] vfs_read+0xc7/0x130 [] sys_read+0x53/0xa0 [] system_call_fastpath+0x16/0x1b Investigation determined that the bug triggered when reading system RAM at the 4G mark. On this system, that was the first address using 1G pages for the virt->phys direct mapping so the PUD is pointing to a physical address, not a PMD page. The problem is that the page table walker in kern_addr_valid() is not checking pud_large() and treats the physical address as if it was a PMD. If it happens to look like pmd_none then it'll silently fail, probably returning zeros instead of real data. If the data happens to look like a present PMD though, it will be walked resulting in the oops above. This patch adds the necessary pud_large() check. Unfortunately the problem was not readily reproducible and now they are running the backup program without accessing /proc/kcore so the patch has not been validated but I think it makes sense. Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel Reviewed-by: Michal Hocko Acked-by: Johannes Weiner Cc: stable@vger.kernel.org Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20130211145236.GX21389@suse.de Signed-off-by: Ingo Molnar --- arch/x86/include/asm/pgtable.h | 5 +++++ arch/x86/mm/init_64.c | 3 +++ 2 files changed, 8 insertions(+) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 5199db2..1c1a955 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -142,6 +142,11 @@ static inline unsigned long pmd_pfn(pmd_t pmd) return (pmd_val(pmd) & PTE_PFN_MASK) >> PAGE_SHIFT; } +static inline unsigned long pud_pfn(pud_t pud) +{ + return (pud_val(pud) & PTE_PFN_MASK) >> PAGE_SHIFT; +} + #define pte_page(pte) pfn_to_page(pte_pfn(pte)) static inline int pmd_large(pmd_t pte) diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index 2ead3c8..75c9a6a 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -831,6 +831,9 @@ int kern_addr_valid(unsigned long addr) if (pud_none(*pud)) return 0; + if (pud_large(*pud)) + return pfn_valid(pud_pfn(*pud)); + pmd = pmd_offset(pud, addr); if (pmd_none(*pmd)) return 0;