linux-kernel - Re: [RFC PATCH 13/16] arm64: mm: Reset pkey in __tlb_remove

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Message-ID: <20241209102913.GJ21636@noisy.programming.kicks-ass.net>
Date: Mon, 9 Dec 2024 11:29:13 +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 13/16] arm64: mm: Reset pkey in __tlb_remove_table()

On Fri, Dec 06, 2024 at 10:11:07AM +0000, Kevin Brodsky wrote:
> Page table pages are typically freed via tlb_remove_table() and
> friends. Ensure that the linear mapping for those pages is reset to
> the default pkey when CONFIG_KPKEYS_HARDENED_PGTABLES is enabled.
> 
> This patch is a no-op if CONFIG_KPKEYS_HARDENED_PGTABLES is disabled
> (default).
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
> ---
>  arch/arm64/include/asm/tlb.h | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> index a947c6e784ed..d1611ffa6d91 100644
> --- a/arch/arm64/include/asm/tlb.h
> +++ b/arch/arm64/include/asm/tlb.h
> @@ -10,10 +10,14 @@
>  
>  #include <linux/pagemap.h>
>  #include <linux/swap.h>
> +#include <linux/kpkeys.h>
>  
>  static inline void __tlb_remove_table(void *_table)
>  {
> -	free_page_and_swap_cache((struct page *)_table);
> +	struct page *page = (struct page *)_table;
> +
> +	kpkeys_unprotect_pgtable_memory((unsigned long)page_address(page), 1);
> +	free_page_and_swap_cache(page);
>  }

Same as for the others, perhaps stick this in generic code instead of in
the arch code?