[PATCH RFC v9 11/25] mm: kpkeys: Introduce kpkeys_hardened_pgtables feature

[Kevin Brodsky]

On 07/09/2026 12:54, Mike Rapoport wrote:
> Hi Kevin,
>
>> kpkeys_hardened_pgtables is a hardening feature based on kpkeys. It
>> aims to prevent the corruption of page tables by: 1. mapping all
>> page table pages, both kernel and user, with a privileged pkey
>> (KPKEYS_PKEY_PGTABLES), and 2. granting write access to that pkey
>> only when running at in a privileged kpkeys context
>> (KPKEYS_CTX_PGTABLES). This patch introduces basic infrastructure;
>> the implementation of both aspects will follow.
>>
>> The feature is exposed as CONFIG_KPKEYS_HARDENED_PGTABLES; it
>> requires explicit architecture opt-in by selecting
>> ARCH_HAS_KPKEYS_HARDENED_PGTABLES, since much of the page table
>> handling is arch-specific.
>>
>> Because this feature relies on kpkeys being supported and modifies
>> attributes of the linear map, it must be inactive on boot.
>> kpkeys_hardened_pgtables_init() enables it by toggling a static key;
>> this function must be called by supported architectures in
>> mem_init(), before any call to pagetable_alloc() is made.
> Presuming other architecures will use kpkeys framework it's better to
> call kpkeys_hardened_pgtables_init() from mm_core_init() rather than
> stick into each arch's mem_init().

Ah yes I was wondering whether it was acceptable to stick another call
directly in mm_core_init(), but I suppose it doesn't hurt. I can move
the call to kpkeys_hardened_pgtables_init() just before
memblock_free_all() and leave mem_init() alone.

Thanks for chipping in!

- Kevin