This is a note to let you know that I've just added the patch titled
xen/pte: Fix crashes when trying to see non-existent PGD/PMD/PUD/PTEs
to the 3.3-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:
xen-pte-fix-crashes-when-trying-to-see-non-existent-pgd-pmd-pud-ptes.patch
and it can be found in the queue-3.3 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From b7e5ffe5d83fa40d702976d77452004abbe35791 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <[email protected]>
Date: Thu, 3 May 2012 16:14:14 -0400
Subject: xen/pte: Fix crashes when trying to see non-existent PGD/PMD/PUD/PTEs
From: Konrad Rzeszutek Wilk <[email protected]>
commit b7e5ffe5d83fa40d702976d77452004abbe35791 upstream.
If I try to do "cat /sys/kernel/debug/kernel_page_tables"
I end up with:
BUG: unable to handle kernel paging request at ffffc7fffffff000
IP: [<ffffffff8106aa51>] ptdump_show+0x221/0x480
PGD 0
Oops: 0000 [#1] SMP
CPU 0
.. snip..
RAX: 0000000000000000 RBX: ffffc00000000fff RCX: 0000000000000000
RDX: 0000800000000000 RSI: 0000000000000000 RDI: ffffc7fffffff000
which is due to the fact we are trying to access a PFN that is not
accessible to us. The reason (at least in this case) was that
PGD[256] is set to __HYPERVISOR_VIRT_START which was setup (by the
hypervisor) to point to a read-only linear map of the MFN->PFN array.
During our parsing we would get the MFN (a valid one), try to look
it up in the MFN->PFN tree and find it invalid and return ~0 as PFN.
Then pte_mfn_to_pfn would happilly feed that in, attach the flags
and return it back to the caller. 'ptdump_show' bitshifts it and
gets and invalid value that it tries to dereference.
Instead of doing all of that, we detect the ~0 case and just
return !_PAGE_PRESENT.
This bug has been in existence .. at least until 2.6.37 (yikes!)
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/x86/xen/mmu.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -353,8 +353,13 @@ static pteval_t pte_mfn_to_pfn(pteval_t
{
if (val & _PAGE_PRESENT) {
unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
+ unsigned long pfn = mfn_to_pfn(mfn);
+
pteval_t flags = val & PTE_FLAGS_MASK;
- val = ((pteval_t)mfn_to_pfn(mfn) << PAGE_SHIFT) | flags;
+ if (unlikely(pfn == ~0))
+ val = flags & ~_PAGE_PRESENT;
+ else
+ val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
}
return val;
Patches currently in stable-queue which might be from [email protected] are
queue-3.3/xen-pte-fix-crashes-when-trying-to-see-non-existent-pgd-pmd-pud-ptes.patch
queue-3.3/xen-pci-don-t-use-pci-bios-service-for-configuration-space-accesses.patch
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