linux-kernel - Re: [RFC PATCH 08/16] mm: Introduce kernel_pgtables_set

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Message-ID: <20241209100335.GH21636@noisy.programming.kicks-ass.net>
Date: Mon, 9 Dec 2024 11:03:35 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
	aruna.ramakrishna@...cle.com, broonie@...nel.org,
	catalin.marinas@....com, dave.hansen@...ux.intel.com,
	jannh@...gle.com, jeffxu@...omium.org, joey.gouly@....com,
	kees@...nel.org, maz@...nel.org, pierre.langlois@....com,
	qperret@...gle.com, ryan.roberts@....com, will@...nel.org,
	linux-arm-kernel@...ts.infradead.org, x86@...nel.org
Subject: Re: [RFC PATCH 08/16] mm: Introduce kernel_pgtables_set_pkey()

On Fri, Dec 06, 2024 at 10:11:02AM +0000, Kevin Brodsky 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>
> ---
> 
> It feels that some sort of locking is called for in
> kernel_pgtables_set_pkey(), but I couldn't figure out what would be
> appropriate.

init_mm.page_table_lock is typically the one used to serialize kernel
page tables IIRC.