Patchwork [3.5.y.z,extended,stable] Patch "x86/mm: Check if PUD is large when validating a kernel" has been added to staging queue

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Submitter Herton Ronaldo Krzesinski
Date Feb. 15, 2013, 5:03 p.m.
Message ID <1360947794-25402-1-git-send-email-herton.krzesinski@canonical.com>
Download mbox | patch
Permalink /patch/220777/
State New
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Comments

Herton Ronaldo Krzesinski - Feb. 15, 2013, 5:03 p.m.
This is a note to let you know that I have just added a patch titled

    x86/mm: Check if PUD is large when validating a kernel

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

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From 6188e408d02d10d48f193d357e271ac9a046871a Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Mon, 11 Feb 2013 14:52:36 +0000
Subject: [PATCH] x86/mm: Check if PUD is large when validating a kernel
 address

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: [<ffffffff8103157e>] kern_addr_valid+0xbe/0x110
 [...]

 Call Trace:
  [<ffffffff811b8aaa>] read_kcore+0x17a/0x370
  [<ffffffff811ad847>] proc_reg_read+0x77/0xc0
  [<ffffffff81151687>] vfs_read+0xc7/0x130
  [<ffffffff811517f3>] sys_read+0x53/0xa0
  [<ffffffff81449692>] 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 <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.coM>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20130211145236.GX21389@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
---
 arch/x86/include/asm/pgtable.h |    5 +++++
 arch/x86/mm/init_64.c          |    3 +++
 2 files changed, 8 insertions(+)

--
1.7.9.5

Patch

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;