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

[Kees Cook]

On Mon, Nov 20, 2017 at 10:45 AM, Florian Fainelli <f.fainelli at gmail.com> wrote:
> On 11/08/2017 04:41 PM, Philip Derrin 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.
>
> FWIW, on an ARCH_BRCMSTB system with ARM_LPAE=y:
>
> Tested-by: Florian Fainelli <f.fainelli at gmail.com>

Russell, given this fixes an accidentally broken feature, is there any
hope for this series to land in v4.15?

Thanks!

-Kees

-- 
Kees Cook
Pixel Security