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

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commit ba385c0594 upstream.

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.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

...

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Gerald Schaefer 2017-09-18 16:51:51 +02:00 • committed by Ben Hutchings

parent 19d1b47bd1

commit 7bb28761f4

1 changed files with 3 additions and 4 deletions

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arch/s390/mm/gup.c

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