ARM: 8721/1: mm: dump: check hardware RO bit for LPAE
authorPhilip Derrin <philip@cog.systems>
Mon, 13 Nov 2017 23:55:26 +0000 (00:55 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 30 Nov 2017 08:40:40 +0000 (08:40 +0000)
commit30d3389d80eb0c6d2a49ffa07c8fd1eec5a49873
tree887cc51c33fbb7c07e685dcc14a4f87ee057e750
parentcb7cc998a0e5f0f4572609ccc334de5a6260b406
ARM: 8721/1: mm: dump: check hardware RO bit for LPAE

commit 3b0c0c922ff4be275a8beb87ce5657d16f355b54 upstream.

When CONFIG_ARM_LPAE is set, the PMD dump relies on the software
read-only bit to determine whether a page is writable. This
concealed a bug which left the kernel text section writable
(AP2=0) while marked read-only in the software bit.

In a kernel with the AP2 bug, the dump looks like this:

    ---[ Kernel Mapping ]---
    0xc0000000-0xc0200000           2M RW NX SHD
    0xc0200000-0xc0600000           4M ro x  SHD
    0xc0600000-0xc0800000           2M ro NX SHD
    0xc0800000-0xc4800000          64M RW NX SHD

The fix is to check that the software and hardware bits are both
set before displaying "ro". The dump then shows the true perms:

    ---[ Kernel Mapping ]---
    0xc0000000-0xc0200000           2M RW NX SHD
    0xc0200000-0xc0600000           4M RW x  SHD
    0xc0600000-0xc0800000           2M RW NX SHD
    0xc0800000-0xc4800000          64M RW NX SHD

Fixes: ded947798469 ("ARM: 8109/1: mm: Modify pte_write and pmd_write logic for LPAE")
Signed-off-by: Philip Derrin <philip@cog.systems>
Tested-by: Neil Dick <neil@cog.systems>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/arm/mm/dump.c