linux-kernel - Re: [PATCH v1] hugetlb: support FOLL_FORCE|FOLL

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: <77838f94-f333-4973-858f-ea2964ea7b9e@redhat.com>
Date: Wed, 4 Dec 2024 20:30:14 +0100
From: David Hildenbrand <david@...hat.com>
To: Guillaume Morin <guillaume@...infr.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Muchun Song <muchun.song@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>, Peter Xu <peterx@...hat.com>,
 Eric Hagberg <ehagberg@...estreet.com>
Subject: Re: [PATCH v1] hugetlb: support FOLL_FORCE|FOLL_WRITE

On 04.12.24 20:13, Guillaume Morin wrote:
> On 04 Dec 20:01, David Hildenbrand wrote:
>>
>> On 04.12.24 19:26, Guillaume Morin wrote:
>>
>> Patch prefix should likely be "mm/hugetlb: ..."
>>
>>> FOLL_FORCE|FOLL_WRITE has never been properly supported for hugetlb
>>> mappings.  Since 1d8d14641fd94, we explicitly reject it. However
>>
>> "Since commit 1d8d14641fd9 ("mm/hugetlb: support write-faults in shared
>> mappings") ..."
> 
> Will fix in v2.
> 
>>
>>> running software on hugetlb mappings is a useful optimization.
>>> Multiple tools allow to use that such as Intel iodlr or
>>> libhugetlbfs.
>>
>> It would be better to link to the actual request where people ran into that
>> when using PTRACE_POKETEXT
>>
>> That hugetlb is getting used is rather obvious :)
> 
> Well, allow me to point out that I said running software on a hugetlb
> mapping, not generally using hugetlb.

Well, yes, but that's not really big news. People have been doing that 
(and rewriting their apps using libhugetlbfs to place text on huge pages 
pre file THP) for decades. :)

See below.

> 
> That said, which link are you referring to? The only discussion I am
> aware of is off mailing lists.

Oh, indeed, I could have sworn it was public.

I'd write something like

"Eric reported that PTRACE_POKETEXT fails when applications use hugetlb 
for mapping text using huge pages. Before commit 1d8d14641fd9, 
PTRACE_POKETEXT worked by accident, but it was buggy and silently ended 
up mapping pages writable into the page tables even though VM_WRITE was 
not set.

In general, FOLL_FORCE|FOLL_WRITE does currently not work with hugetlb. 
Let's implement FOLL_FORCE|FOLL_WRITE properly for hugetlb, such that 
what used to work in the past by accident now properly works, allowing 
applications using hugetlb for text etc. to get properly debugged.

This change might also be required to implement uprobes support for 
hugetlb [1].

[1] link to our discussion
"

-- 
Cheers,

David / dhildenb