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authorHugh Dickins <hughd@google.com>2016-02-17 13:11:23 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-02-18 16:23:24 -0800
commit457a98b0809fa6cde7aab8c314a59d99772b445e (patch)
tree61fd434ac02707ba73f84db22a802215dd8469cf
parent0918f1c309b86301605650c836ddd2021d311ae2 (diff)
mm, x86: fix pte_page() crash in gup_pte_range()
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>
-rw-r--r--arch/x86/mm/gup.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index 6d5eb5900372..d8a798d8bf50 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -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);