linux-kernel - Re: [PATCH 06/14] mm: handle_pte_fault() use pte_offset_map_maywrite

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <38d6caeb-1aba-43d2-8daf-12b9aaba77bd@redhat.com>
Date: Thu, 22 Aug 2024 14:19:01 +0200
From: David Hildenbrand <david@...hat.com>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: LEROY Christophe <christophe.leroy2@...soprasteria.com>,
 "hughd@...gle.com" <hughd@...gle.com>,
 "willy@...radead.org" <willy@...radead.org>,
 "muchun.song@...ux.dev" <muchun.song@...ux.dev>,
 "vbabka@...nel.org" <vbabka@...nel.org>,
 "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
 "rppt@...nel.org" <rppt@...nel.org>,
 "vishal.moola@...il.com" <vishal.moola@...il.com>,
 "peterx@...hat.com" <peterx@...hat.com>,
 "ryan.roberts@....com" <ryan.roberts@....com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 06/14] mm: handle_pte_fault() use
 pte_offset_map_maywrite_nolock()

On 22.08.24 14:17, Qi Zheng wrote:
> Hi David,
> 
> On 2024/8/22 17:29, David Hildenbrand wrote:
>> On 21.08.24 12:03, Qi Zheng wrote:
>>>
>>>
> 
> [...]
> 
>>>>>>>>> -        vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm,
>>>>>>>>> vmf->pmd,
>>>>>>>>> -                         vmf->address, &vmf->ptl);
>>>>>>>>> +        vmf->pte = pte_offset_map_maywrite_nolock(vmf->vma->vm_mm,
>>>>>>>>> +                              vmf->pmd, vmf->address,
>>>>>>>>> +                              NULL, &vmf->ptl);
>>>>>>
>>>>>> I think we discussed that passing NULL should be forbidden for that
>>>>>> function.
>>>>>
>>>>> Yes, but for some maywrite case, there is no need to get pmdval to
>>>>> do pmd_same() check. So I passed NULL and added a comment to
>>>>> explain this.
>>>>
>>>> I wonder if it's better to pass a dummy variable instead. One has to
>>>> think harder why that is required compared to blindly passing "NULL" :)
>>>
>>> You are afraid that subsequent caller will abuse this function, right?
>>
>> Yes! "oh, I don't need a pmdval, why would I? let's just pass NULL,
>> easy" :)
>>
>>> My initial concern was that this would add a useless local vaiable, but
>>> perhaps that is not a big deal.
>>
>> How many of these "special" instances do we have?
> 
> We have 5 such special instances.
> 
>>
>>>
>>> Both are fine for me. ;)
>>
>> Also no strong opinion, but having to pass a variable makes you think
>> what you are supposed to do with it and why it is not optional.
> 
> Yeah, I added 'BUG_ON(!pmdvalp);' in pte_offset_map_ro_nolock(), and
> have updated the v2 version [1].

No BUG_ON please :) VM_WARN_ON_ONCE() is good enough.

-- 
Cheers,

David / dhildenb