From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx142.postini.com [74.125.245.142]) by kanga.kvack.org (Postfix) with SMTP id A255D6B0005 for ; Tue, 19 Feb 2013 13:55:07 -0500 (EST) From: Herton Ronaldo Krzesinski Subject: [PATCH 78/81] x86/mm: Check if PUD is large when validating a kernel address Date: Tue, 19 Feb 2013 15:49:41 -0300 Message-Id: <1361299784-8830-79-git-send-email-herton.krzesinski@canonical.com> In-Reply-To: <1361299784-8830-1-git-send-email-herton.krzesinski@canonical.com> References: <1361299784-8830-1-git-send-email-herton.krzesinski@canonical.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Mel Gorman , linux-mm@kvack.org, Ingo Molnar , Herton Ronaldo Krzesinski 3.5.7.6 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Mel Gorman 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: Herton Ronaldo Krzesinski --- 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 c3520d7..3f3dd52 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 3baff25..ce42da7 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -829,6 +829,9 @@ 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; -- 1.7.9.5 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org