arm64: Ignore the 'write' ESR flag on cache maintenance faults

arm64: Ignore the 'write' ESR flag on cache maintenance faults

commit 0e7f7bcc3fc87489cda5aa6aff8ce40eed912279 upstream.

ESR.WnR bit is always set on data cache maintenance faults even though
the page is not required to have write permission. If a translation
fault (page not yet mapped) happens for read-only user address range,
Linux incorrectly assumes a permission fault. This patch adds the check
of the ESR.CM bit during the page fault handling to ignore the 'write'
flag.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Tim Northover <Tim.Northover@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>