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authorMel Gorman <mgorman@suse.de>2013-02-11 14:52:36 +0000
committerBen Hutchings <ben@decadent.org.uk>2013-03-06 03:23:56 +0000
commit7ee959779fbb0ac92d264c88e53eac3628cfcc1f (patch)
treea60cc74d11e1f79b4f3d663fdc2161b0178a979c /arch/x86/mm
parent12324875d79c23a13bbf66390b595a84337dc8d7 (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: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'arch/x86/mm')
-rw-r--r--arch/x86/mm/init_64.c3
1 files changed, 3 insertions, 0 deletions
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;