Re: [PATCH v2] module: Extend module_blacklist parameter to built-in modules

On Mon, Jun 22, 2026 at 10:02:59AM -0400, Aaron Tomlin wrote:
> Currently, the module_blacklist= parameter only prevents
> the dynamic loading of external modules. It possesses no mechanism to
> intercept or prevent the initialisation of built-in modules, as their
> associated initcalls are invoked unconditionally during system boot.
> 
> This patch extends the blacklisting behaviour to encompass built-in
> modules. It introduces a dedicated ".initcall.modnames" section into
> the linker script, systematically mapping each initcall to its
> originating module name. During the boot sequence, do_one_initcall()
> interrogates this mapping; should the executing initcall belong to a
> blacklisted module, its execution is explicitly bypassed.

Hi Arnd, Luis, Petr, Daniel, Sami,

Sashiko [1] correctly reported issues with this version. Consequently,
in the next iteration, I will implement the following changes:

    1.  Abandon the raw assembly approach in favour of using standard C
        structures (i.e., struct initcall_modname). While this sacrifices
        the PREL32 relative offset optimisation for this specific table, it
        guarantees architectural safety and ensures native compiler support
        for both LTO and CFI.

    2.  Wrap the module_is_blacklisted declaration in the necessary #ifdef
        CONFIG_MODULES guards to prevent undefined reference errors when
        loadable module support is disabled.

    3.  Iterating over .initcall.modnames within the shared
        do_one_initcall() path introduces a severe UAF vulnerability when
        loadable modules are initialised post-boot. To rectify this, I will
        introduce a strict, read-only flag (initmem_freed) to explicitly
        bypass the built-in lookup once free_initmem() has reclaimed the
        .init sections. Furthermore, to maintain a clean separation of
        concerns, the blacklist check for loadable modules will be migrated
        directly into the module loader path (do_init_module()).

[1]: https://sashiko.dev/#/patchset/20260622140259.2974-1-atomlin%40atomlin.com


Kind regards,
-- 
Aaron Tomlin