linux-kernel - Re: [PATCH v2 0/5] Use nth_page() in place of direct struct page manipulation

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] [day] [month] [year] [list]

Message-ID: <7122A099-A01A-4B49-8391-E070E661E4B7@nvidia.com>
Date:   Fri, 08 Sep 2023 10:56:46 -0400
From:   Zi Yan <ziy@...dia.com>
To:     "Philippe Mathieu-Daudé" <philmd@...aro.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "\"Matthew Wilcox (Oracle)\"" <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        "\"Mike Rapoport (IBM)\"" <rppt@...nel.org>
Subject: Re: [PATCH v2 0/5] Use nth_page() in place of direct struct page
 manipulation

On 8 Sep 2023, at 10:46, Philippe Mathieu-Daudé wrote:

> Hi,
>
> On 6/9/23 17:03, Zi Yan wrote:
>> From: Zi Yan <ziy@...dia.com>
>>
>> On SPARSEMEM without VMEMMAP, struct page is not guaranteed to be
>> contiguous, since each memory section's memmap might be allocated
>> independently. hugetlb pages can go beyond a memory section size, thus
>> direct struct page manipulation on hugetlb pages/subpages might give
>> wrong struct page. Kernel provides nth_page() to do the manipulation
>> properly. Use that whenever code can see hugetlb pages.
>
> How can we notice "whenever code can see hugetlb pages"?
> From your series it seems you did a manual code audit, is that correct?
> (I ask because I'm wondering about code scalability and catching other
> cases).

Anything allocated from buddy allocator should be free of this problem,
because MAX_ORDER is always smaller than a memory section size. This means
majority of kernel code should be fine. What is left is core mm code that
can have a chance to touch hugetlb, like migration, memory compaction,
and of course hugetlb code. Yes, I did a manual code audit. And hopefully
I caught all cases.

An alternative is to use nth_page() everywhere, but that is a very invasive
change for an uncommon config (SPARSEMEM + !VMEMMAP).


--
Best Regards,
Yan, Zi

Download attachment "signature.asc" of type "application/pgp-signature" (855 bytes)