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mm, x86: fix pte_page() crash in gup_pte_range()

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Commit 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") has
moved up the pte_page(pte) in x86's fast gup_pte_range(), for no
discernible reason: put it back where it belongs, after the pte_flags
check and the pfn_valid cross-check.

That may be the cause of the NULL pointer dereference in
gup_pte_range(), seen when vfio called vaddr_get_pfn() when starting a
qemu-kvm based VM.

Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Michael Long <Harn-Solo@gmx.de>
Tested-by: Michael Long <Harn-Solo@gmx.de>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2016-02-17 13:11:23 -08:00 committed by Linus Torvalds
parent 0918f1c309
commit 457a98b080
1 changed files with 1 additions and 1 deletions
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2
arch/x86/mm/gup.c
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@ -102,7 +102,6 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
return 0;
}
page = pte_page(pte);
if (pte_devmap(pte)) {
pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
if (unlikely(!pgmap)) {
@ -115,6 +114,7 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
return 0;
}
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
get_page(page);
put_dev_pagemap(pgmap);
SetPageReferenced(page);