linux-kernel - Re: [PATCH v2 3/3] module: Make .static_call

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: <3ad23825-d249-4108-b5c3-693e359fd12e@suse.com>
Date: Wed, 12 Mar 2025 13:05:22 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Sami Tolvanen <samitolvanen@...gle.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Jason Baron <jbaron@...mai.com>, Daniel Gomez <da.gomez@...sung.com>,
 Steven Rostedt <rostedt@...dmis.org>, Ard Biesheuvel <ardb@...nel.org>,
 linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] module: Make .static_call_sites read-only after
 init

On 3/7/25 01:12, Sami Tolvanen wrote:
> On Thu, Mar 06, 2025 at 06:28:58PM +0100, Christophe Leroy wrote:
>> Le 06/03/2025 à 14:13, Petr Pavlu a écrit :
>>> Section .static_call_sites holds data structures that need to be sorted and
>>> processed only at module load time. This initial processing happens in
>>> static_call_add_module(), which is invoked as a callback to the
>>> MODULE_STATE_COMING notification from prepare_coming_module().
>>>
>>> The section is never modified afterwards. Make it therefore read-only after
>>> module initialization to avoid any (non-)accidental modifications.
>>
>> Maybe this suggestion is stupid, I didn't investigate the feasability but:
>> why don't we group everything that is ro_after_init in a single section just
>> like we do in vmlinux ? That would avoid having to add every new possible
>> section in the C code.
>>
>> Like we have in asm-generic/vmlinux.lds.h:
>>
>> #define RO_AFTER_INIT_DATA						\
>> 	. = ALIGN(8);							\
>> 	__start_ro_after_init = .;					\
>> 	*(.data..ro_after_init)						\
>> 	JUMP_TABLE_DATA							\
>> 	STATIC_CALL_DATA						\
>> 	__end_ro_after_init = .;
> 
> I like this idea. Grouping the sections in the module linker script
> feels cleaner than having an array of section names in the code. To be
> fair, I think this code predates v5.10, where scripts/module.lds.S was
> first added.

I agree in principle. I like that the information about ro_after_init
sections for vmlinux and modules would be in the same source form, in
linker scripts. This could eventually allow us to share the definition
of ro_after_init sections between vmlinux and modules.

The problem is however how to find the location of the __jump_table and
static_call_sites data. In vmlinux, as a final binary, they are
annotated with start and end symbols. In modules, as relocatable files,
the approach is to rely on them being separate sections, see function
find_module_sections().

I could add start+end symbols for __jump_table and static_call_sites
data in scripts/module.lds.S and use them by the module loader, but this
would create an inconsistency in how various data is looked up. Another
problem is that I can't find a way to tell the linker to add these
symbols only if the specific data is actually present.

-- 
Cheers,
Petr