linux-kernel - Re: [PATCH 1/3] memory: extern memory_block_size_bytes and set_memory_block_size

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: <2c854e5e-c200-4ed9-bf21-778779af7e5b@redhat.com>
Date: Mon, 14 Oct 2024 13:54:27 +0200
From: David Hildenbrand <david@...hat.com>
To: Gregory Price <gourry@...rry.net>
Cc: linux-cxl@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org,
 linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
 dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
 osalvador@...e.de, gregkh@...uxfoundation.org, rafael@...nel.org,
 akpm@...ux-foundation.org, dan.j.williams@...el.com,
 Jonathan.Cameron@...wei.com, alison.schofield@...el.com, rrichter@....com,
 terry.bowman@....com, lenb@...nel.org, dave.jiang@...el.com,
 ira.weiny@...el.com
Subject: Re: [PATCH 1/3] memory: extern memory_block_size_bytes and
 set_memory_block_size_order

On 08.10.24 17:21, Gregory Price wrote:
> On Tue, Oct 08, 2024 at 05:02:33PM +0200, David Hildenbrand wrote:
>> On 08.10.24 16:51, Gregory Price wrote:
>>>>> +int __weak set_memory_block_size_order(unsigned int order)
>>>>> +{
>>>>> +	return -ENODEV;
>>>>> +}
>>>>> +EXPORT_SYMBOL_GPL(set_memory_block_size_order);
>>>>
>>>> I can understand what you are trying to achieve, but letting arbitrary
>>>> modules mess with this sounds like a bad idea.
>>>>
>>>
>>> I suppose the alternative is trying to scan the CEDT from inside each
>>> machine, rather than the ACPI driver?  Seems less maintainable.
>>>
>>> I don't entirely disagree with your comment.  I hummed and hawwed over
>>> externing this - hence the warning in the x86 machine.
>>>
>>> Open to better answers.
>>
>> Maybe an interface to add more restrictions on the maximum size might be
>> better (instead of setting the size/order, you would impose another upper
>> limit).
> 
> That is effectively what set_memory_block_size_order is, though.  Once
> blocks are exposed to the allocators, its no longer safe to change the
> size (in part because it was built assuming it wouldn't change, but I
> imagine there are other dragons waiting in the shadows to bite me).

Yes, we must run very early.

How is this supposed to interact with code like

set_block_size()

that also calls set_memory_block_size_order() on UV systems (assuming 
there will be CXL support sooner or later?)?


> 
> So this would basically amount to a lock-bit being set in the architecture,
> beyond which block size can no longer be changed and a big ol' splat
> can be generated that says "NO TOUCH".
> 
>> Just imagine having various users of such an interface ..
> 
> I don't wanna D:

Right, and it also doesn't make sense as explained in my other comment: 
this should never apply to loaded modules. :)

-- 
Cheers,

David / dhildenb