This is a note to let you know that I've just added the patch titled
x86/mm: Check if PUD is large when validating a kernel address
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-mm-check-if-pud-is-large-when-validating-a-kernel-address.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 0ee364eb316348ddf3e0dfcd986f5f13f528f821 Mon Sep 17 00:00:00 2001
From: Mel Gorman <[email protected]>
Date: Mon, 11 Feb 2013 14:52:36 +0000
Subject: x86/mm: Check if PUD is large when validating a kernel address
From: Mel Gorman <[email protected]>
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 <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Reviewed-by: Michal Hocko <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/x86/include/asm/pgtable.h | 5 +++++
arch/x86/mm/init_64.c | 3 +++
2 files changed, 8 insertions(+)
--- 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_
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)
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -821,6 +821,9 @@ 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;
Patches currently in stable-queue which might be from [email protected] are
queue-3.4/x86-mm-check-if-pud-is-large-when-validating-a-kernel-address.patch
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
