[PATCH 0/2] STRICT_KERNEL_RWX weakened on ARM by CONFIG_ARM_LPAE=y

[Kees Cook]

On Wed, Nov 8, 2017 at 4:41 PM, Philip Derrin <philip at cog.systems> wrote:
> Hi,
>
> This patch series fixes a bug which makes CONFIG_STRICT_KERNEL_RWX ineffective
> when CONFIG_ARM_LPAE is enabled. Specifically, the kernel text and rodata are
> mapped writeable. This has been the case since DEBUG_RODATA for ARM was first
> merged in 3.19.
>
> The cause was an incorrect conflict resolution in 1e3479225acb ("ARM: 8275/1:
> mm: fix PMD_SECT_RDONLY undeclared compile error") between the commit that
> implemented DEBUG_RODATA, 80d6b0c2eed2 ("ARM: mm: allow text and rodata
> sections to be read-only"), and another that moved the LPAE read-only bit into
> a software bit, ded947798469 ("ARM: 8109/1: mm: Modify pte_write and pmd_write
> logic for LPAE").
>
> The incorrect mappings were not apparent in the debugfs kernel_page_tables
> dump because that was checking only the software RO bit, not the hardware RO
> bit.

Thanks for catching this! Please consider both patches:

Reviewed-by: Kees Cook <keescook at chromium.org>

-Kees

>
> Regards,
> Philip
>
>
> Philip Derrin (2):
>   ARM: mm: make STRICT_KERNEL_RWX effective for LPAE
>   ARM: mm: dump: check hardware RO bit for LPAE
>
>  arch/arm/mm/dump.c | 4 ++--
>  arch/arm/mm/init.c | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> --
> 2.15.0
>



-- 
Kees Cook
Pixel Security