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s390/mm: fix write access check in gup_huge_pmd()

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The check for the _SEGMENT_ENTRY_PROTECT bit in gup_huge_pmd() is the
wrong way around. It must not be set for write==1, and not be checked for
write==0. Fix this similar to how it was fixed for ptes long time ago in
commit 25591b0703 ("[S390] fix get_user_pages_fast").

One impact of this bug would be unnecessarily using the gup slow path for
write==0 on r/w mappings. A potentially more severe impact would be that
gup_huge_pmd() will succeed for write==1 on r/o mappings.

Cc: <stable@vger.kernel.org>
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Gerald Schaefer 2017-09-18 16:51:51 +02:00 committed by Martin Schwidefsky
parent 91c575b335
commit ba385c0594
1 changed files with 3 additions and 4 deletions
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7
arch/s390/mm/gup.c
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@ -56,13 +56,12 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
unsigned long mask, result;
struct page *head, *page;
unsigned long mask;
int refs;
result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
mask = result | _SEGMENT_ENTRY_INVALID;
if ((pmd_val(pmd) & mask) != result)
mask = (write ? _SEGMENT_ENTRY_PROTECT : 0) | _SEGMENT_ENTRY_INVALID;
if ((pmd_val(pmd) & mask) != 0)
return 0;
VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));