Ram Pai [off-list ref] writes:

Pkey tracking information is not copied over to the mm_struct of the
child during fork(). This can cause the child to erroneously allocate
keys that were already allocated. Any allocated execute-only key is lost
aswell.
    
Add code; called by dup_mmap(), to copy the pkey state from parent to
child explicitly.
    
This problem was originally found by Dave Hansen on x86, which turns out
to be a problem on powerpc aswell.
    
Reviewed-by: Thiago Jung Bauermann <redacted>
Signed-off-by: Ram Pai <redacted>
    
v2: do not copy if pkeys is disabled.
    	-- comment by Michael Ellermen

Thanks.

I changed the subject to:

  powerpc/pkeys: Fix handling of pkey state across fork()

And added tags:

  Fixes: cf43d3b26452 ("powerpc: Enable pkey subsystem")
  Cc: stable@vger.kernel.org # v4.16+

cheers