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

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Message-ID: <a8fea276-152f-4cf3-a87f-e48ae6e5c024@arm.com>
Date: Wed, 11 Dec 2024 14:37:38 +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 10/12/2024 13:27, Peter Zijlstra wrote:
> On Tue, Dec 10, 2024 at 10:28:44AM +0100, Kevin Brodsky wrote:
>> 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.
> I don't foresee other __tlb_remove_table() users, this is all rather
> speicific code. But if there ever were to be new users, it is something
> they would have to take into consideration.

Fair enough, I'll handle that in mm/mmu_gather.c then.

- Kevin