Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932654AbaBEUp3 (ORCPT ); Wed, 5 Feb 2014 15:45:29 -0500 Received: from mail1.windriver.com ([147.11.146.13]:48299 "EHLO mail1.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751515AbaBEUGV (ORCPT ); Wed, 5 Feb 2014 15:06:21 -0500 From: Paul Gortmaker To: , CC: Mel Gorman , , Ingo Molnar , Paul Gortmaker Subject: [v2.6.34-stable 111/213] x86/mm: Check if PUD is large when validating a kernel address Date: Wed, 5 Feb 2014 15:01:06 -0500 Message-ID: <1391630568-49251-112-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.8.5.2 In-Reply-To: <1391630568-49251-1-git-send-email-paul.gortmaker@windriver.com> References: <1391630568-49251-1-git-send-email-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Mel Gorman ------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. ------------------- commit 0ee364eb316348ddf3e0dfcd986f5f13f528f821 upstream. 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: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20130211145236.GX21389@suse.de Signed-off-by: Ingo Molnar Signed-off-by: Paul Gortmaker --- 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 a34c785c5a63..321d24d6a924 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -132,6 +132,11 @@ 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 ee41bba315d1..3cd243b8b01d 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -864,6 +864,9 @@ 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; -- 1.8.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/