diff options
| author | Mel Gorman <mgorman@suse.de> | 2013-02-11 14:52:36 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-02-17 10:46:20 -0800 |
| commit | ec3918604c896df59632d47bd2ed874cbc2f262b (patch) | |
| tree | 4b115fab4ea52bdffd049fa103d49da56fd5eb6c | |
| parent | 54ea5b40f067cf098cac639973c6628c6944cfb2 (diff) | |
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/x86/include/asm/pgtable.h | 5 | ||||
| -rw-r--r-- | arch/x86/mm/init_64.c | 3 |
2 files changed, 8 insertions, 0 deletions
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 884507e68ab..6be990922d4 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 bbaaa005bf0..44b93da1840 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; |