linux-kernel - Re: [PATCH v2 2/5] mm: add PTE_MARKER

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: <e29e6618-4985-492e-81cf-53782550eb33@redhat.com>
Date: Mon, 21 Oct 2024 19:21:46 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Suren Baghdasaryan <surenb@...gle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Matthew Wilcox <willy@...radead.org>, "Paul E . McKenney"
 <paulmck@...nel.org>, Jann Horn <jannh@...gle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Muchun Song <muchun.song@...ux.dev>,
 Richard Henderson <richard.henderson@...aro.org>,
 Ivan Kokshaysky <ink@...assic.park.msu.ru>, Matt Turner
 <mattst88@...il.com>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
 Helge Deller <deller@....de>, Chris Zankel <chris@...kel.net>,
 Max Filippov <jcmvbkbc@...il.com>, Arnd Bergmann <arnd@...db.de>,
 linux-alpha@...r.kernel.org, linux-mips@...r.kernel.org,
 linux-parisc@...r.kernel.org, linux-arch@...r.kernel.org,
 Shuah Khan <shuah@...nel.org>, Christian Brauner <brauner@...nel.org>,
 linux-kselftest@...r.kernel.org, Sidhartha Kumar
 <sidhartha.kumar@...cle.com>, Jeff Xu <jeffxu@...omium.org>,
 Christoph Hellwig <hch@...radead.org>, linux-api@...r.kernel.org,
 John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v2 2/5] mm: add PTE_MARKER_GUARD PTE marker

>>
>>>
>>>>
>>>>>
>>>>> Also the existing logic is that existing markers (HW poison, uffd-simulated HW
>>>>> poison, uffd wp marker) are retained and no error raised on MADV_DONTNEED, and
>>>>> no error on MADV_FREE either, so it'd be consistent with existing behaviour.
>>>>
>>>>
>>>> HW poison / uffd-simulated HW poison are expected to be zapped: it's just
>>>> like a mapped page with HWPOISON. So that is correct.
>>>
>>> Well, poison is _not_ zapped on MADV_DONTNEED but _is_ on MADV_FREE :) anyway, I
>>
>> Huh?
>>
>> madvise_dontneed_single_vma()->zap_page_range_single(details=NULL)->unmap_single_vma(details=NULL)
>> ... zap_pte_range()
>>
>> } else if (is_hwpoison_entry(entry) ||
>> 	   is_poisoned_swp_entry(entry)) {
>> 	if (!should_zap_cows(details))
>> 		continue;
>> 	...
>>
>> Should just zap them.
>>
>> What am I missing?
> 
> Yeah ok it's me who's missing something here, I hadn't noticed details == NULL
> so should_zap_cows() is true, my mistake!

It's confusing code ... I once had a patch to call it 
"should_zap_anon_folios" etc, but it would only slightly make it clearer 
what is actually happening.

> 
> In any case we explicitly add code here to prevent guard pages from going. I
> will correct everything where I wrongly say otherwise, doh!

Right, that's also one of the reasons I don't think "poison" terminology 
is the best fit, because there are som subtle differences. At least the 
marker does not mention "poison" but PTE_MARKER_GUARD, which I think is 
a very good naming :)

-- 
Cheers,

David / dhildenb