ARM: mm: introduce present, faulting entries for PAGE_NONE
commit
26ffd0d43b186b0d5186354da8714a1c2d360df0 upstream.
PROT_NONE mappings apply the page protection attributes defined by _P000
which translate to PAGE_NONE for ARM. These attributes specify an XN,
RDONLY pte that is inaccessible to userspace. However, on kernels
configured without support for domains, such a pte *is* accessible to
the kernel and can be read via get_user, allowing tasks to read
PROT_NONE pages via syscalls such as read/write over a pipe.
This patch introduces a new software pte flag, L_PTE_NONE, that is set
to identify faulting, present entries.
Signed-off-by: Will Deacon <will.deacon@arm.com>
[bwh: Backported to 3.2 as dependency of commit
b6ccb9803e90
('ARM: 7954/1: mm: remove remaining domain support from ARMv6'):
- Drop 3-level changes
- Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>