linux-kernel - Re: [PATCH v5 18/39] mm: Handle faultless write upgrades for shstk

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Date:   Wed, 1 Feb 2023 19:03:49 +0100
From:   David Hildenbrand <david@...hat.com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "bsingharora@...il.com" <bsingharora@...il.com>,
        "hpa@...or.com" <hpa@...or.com>,
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Cc:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v5 18/39] mm: Handle faultless write upgrades for shstk

On 01.02.23 18:32, Edgecombe, Rick P wrote:
> On Wed, 2023-02-01 at 10:03 +0100, David Hildenbrand wrote:
>>>
>>> The other problem is that one of NULL passers is not for kernel
>>> memory.
>>> huge_pte_mkwrite() calls pte_mkwrite(). Shadow stack memory can't
>>> be
>>> created with MAP_HUGETLB, so it is not needed. Using
>>> pte_mkwrite_kernel() would look weird in this case, but making
>>> huge_pte_mkwrite() take a VMA would be for no reason. Maybe making
>>> huge_pte_mkwrite() take a VMA is the better of those two options.
>>> Or
>>> keep the NULL semantics...  Any thoughts?
>>
>> Well, the reason would be consistency. From a core-mm point of view
>> it
>> makes sense to handle this all consistency, even if the single user
>> (x86) wouldn't strictly require it right now.
>>
>> I'd just pass in the VMA and call it a day :)
> 
> Ok, I'll give it a spin.

It would be good to get more opinions on that, but I'm afraid we won't 
get more deep down in this thread :)

-- 
Thanks,

David / dhildenb