Re: [PATCH v3] module: Extend module_blacklist parameter to built-in modules

[Aaron Tomlin]

On Mon, Jul 06, 2026 at 01:03:37AM -0400, Aaron Tomlin wrote:
> Currently, the "module_blacklist=" command-line parameter only applies to
> loadable modules. If a module is built-in, the parameter is silently
> ignored. This patch extends the blacklisting functionality to built-in
> modules by intercepting their initialization routines during early boot.
> 
> To achieve this, we introduce a new ".initcall.modnames" memory section.
> For each built-in module, we use a standard C structure (i.e., struct
> initcall_modname) to map its initcall function pointer to its associated
> KBUILD_MODNAME string.
> 
> During boot, do_one_initcall() cross-references the initcall function
> pointer against this table. If a match is found and the module is
> present in the blacklist, the initcall is skipped.

Hi Arnd, Luis, Petr, Daniel, Sami,

Please ignore. I will send a v4.

Sashiko [1] correctly reported further issues (e.g., CONFIG_MODULES=n)
which have been addressed as follows:

 - Decoupled the module_blacklist parameter parsing and the
   module_is_blacklisted() function from CONFIG_MODULES, moving the
   logic to init/main.c. This ensures the blacklist works for built-in
   modules even on monolithic kernels built without loadable module
   support (CONFIG_MODULES=n)

 - Removed the conditional stub implementation of
   module_is_blacklisted() in module.h and replaced it with a single,
   unconditional declaration outside of the #ifdef CONFIG_MODULES block.
   This prevents compiler warnings about missing prototypes and ensures
   visibility under a monolithic configuration

 - Replaced the initmem_freed state variable and its synchronisation
   logic in kernel_init() with race-free spatial boundary checks using
   is_kernel_text() and is_kernel_inittext() in initcall_get_modname() .

 - Aligned the .initcall_modnames table with relocations by assigning
   .initcall_fn using the __initcall_stub() helper in
   ___define_initcall(). This ensures the lookup matches the actual stub
   pointer passed to do_one_initcall() when
   CONFIG_HAVE_ARCH_PREL32_RELOCATIONS is enabled

 - Updated initcall_get_modname() in main.c to resolve the function
   pointer fn using dereference_function_descriptor(fn) prior to
   checking the .text and .init.text boundaries

[1]: https://sashiko.dev/#/patchset/20260706050337.7613-1-atomlin%40atomlin.com
-- 
Aaron Tomlin