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

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Message-ID: <7124d7f4-1d4c-4497-94d8-243af2ed071a@arm.com>
Date: Tue, 10 Dec 2024 10:28:44 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Peter Zijlstra <peterz@...radead.org>
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 09/12/2024 11:29, Peter Zijlstra wrote:
> On Fri, Dec 06, 2024 at 10:11:07AM +0000, Kevin Brodsky wrote:
>> [...]
>>
>> 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?

This should be doable, with some refactoring. __tlb_remove_table() is
currently called from two functions in mm/mmu_gather.c, I suppose I
could create a wrapper there that calls
kpkeys_unprotect_pgtable_memory() and then __tlb_remove_table(). Like in
the p4d case I do however wonder how robust this is, as
__tlb_remove_table() could end up being called from other places.

- Kevin