linux-hardening - Re: [RFC PATCH v3 08/15] mm: Introduce kernel_pgtables_set

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Message-ID: <CACRpkdZ_eGsfZh2vkG8dtSyZDbStMfDUuj7s7TQ4FcDwThJVkg@mail.gmail.com>
Date: Thu, 6 Feb 2025 20:01:34 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Mark Brown <broonie@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Jann Horn <jannh@...gle.com>, Jeff Xu <jeffxu@...omium.org>, Joey Gouly <joey.gouly@....com>, 
	Kees Cook <kees@...nel.org>, Andy Lutomirski <luto@...nel.org>, Marc Zyngier <maz@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Pierre Langlois <pierre.langlois@....com>, 
	Quentin Perret <qperret@...gle.com>, "Mike Rapoport (IBM)" <rppt@...nel.org>, 
	Ryan Roberts <ryan.roberts@....com>, Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, 
	Matthew Wilcox <willy@...radead.org>, Qi Zheng <zhengqi.arch@...edance.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [RFC PATCH v3 08/15] mm: Introduce kernel_pgtables_set_pkey()

Hi Kevin,

thanks for your patch!

On Mon, Feb 3, 2025 at 11:20 AM Kevin Brodsky <kevin.brodsky@....com> wrote:

> kernel_pgtables_set_pkey() allows setting the pkey of all page table
> pages in swapper_pg_dir, recursively. This will be needed by
> kpkeys_hardened_pgtables, as it relies on all PTPs being mapped with
> a non-default pkey. Those initial kernel page tables cannot
> practically be assigned a non-default pkey right when they are
> allocated, so mutating them during (early) boot is required.
>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>

(...)

> +static int set_page_pkey(void *p, int pkey)
> +static int set_pkey_pte(pmd_t *pmd, int pkey)
> +static int set_pkey_pmd(pud_t *pud, int pkey)
> +static int set_pkey_pud(p4d_t *p4d, int pkey)
> +static int set_pkey_p4d(pgd_t *pgd, int pkey)
> +int kernel_pgtables_set_pkey(int pkey)

Aren't these all discardable after boot, so the whole set should
be tagged with __init?

Other than that it LGTM.

Yours,
Linus Walleij