On Fri Sep 4, 2026 at 3:34 PM BST, Aaron Tomlin wrote:
> On Thu, Sep 03, 2026 at 07:13:02PM +0000, [email protected] wrote:
>> commit 828a4fa4f29a0a3c5aba9065f4ba35eb845dddef
>> Author: Aaron Tomlin <[email protected]>
>>
>> module: Extend module_blacklist parameter to built-in modules
>>
>> This commit extends the module_blacklist command-line parameter to apply to
>> built-in modules. It achieves this by creating a new .initcall.modnames
>> section to map initcalls to module names, intercepting blacklisted builtin
>> initcalls during early boot.
>>
>> > diff --git a/include/asm-generic/vmlinux.lds.h
>> > b/include/asm-generic/vmlinux.lds.h
>> > index b2988aa12f664..7490278b7a2df 100644
>> > --- a/include/asm-generic/vmlinux.lds.h
>> > +++ b/include/asm-generic/vmlinux.lds.h
>> > @@ -734,7 +734,8 @@
>> > EARLYCON_TABLE() \
>> > LSM_TABLE() \
>> > EARLY_LSM_TABLE() \
>> > - KUNIT_INIT_TABLE()
>> > + KUNIT_INIT_TABLE() \
>> > + BOUNDED_SECTION_BY(.initcall.modnames, _initcall_modnames)
>>
>> [Severity: High]
>> Does this section declaration need an alignment constraint? Without a
>> preceding
>> . = ALIGN(8); or similar, the __start_initcall_modnames label might capture
>> the unaligned location counter before padding is inserted by the linker.
>>
>> When iterating over this section during early boot in do_initcall_level(),
>> could the kernel read padding bytes as garbage pointers, breaking the
>> builtin module blacklist feature or causing an unaligned memory access panic?
>
> Hi Petr,
>
> I forgot to restore ". = ALIGN(8)" in this iteration.
>
> The following ensures the location counter . within .init.data is aligned
> to an 8-byte boundary before __start_initcall_modnames = . is captured,
> preventing any linker padding from preceding the first element of the
> table.
Have you observed cases where this as an actual problem?
I suppose this could be fixed in the BOUNDED_SECTION_BY instead by doing
. = ALIGN(ALIGNOF(NEXT_SECTION));
>
> Are you okay with the following?
>
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -735,6 +735,7 @@
> LSM_TABLE() \
> EARLY_LSM_TABLE() \
> KUNIT_INIT_TABLE() \
> + . = ALIGN(8); \
> BOUNDED_SECTION_BY(.initcall.modnames, _initcall_modnames)
>
> #define INIT_TEXT \
>
>
>> > diff --git a/rust/macros/module.rs b/rust/macros/module.rs
>> > index bc7027f8dbb2c..a96157598197f 100644
>> > --- a/rust/macros/module.rs
>> > +++ b/rust/macros/module.rs
>> [ ... ]
>> > @@ -591,6 +594,20 @@ pub extern "C" fn cleanup_module() {
>> > #[cfg(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)]
>> > ::core::arch::global_asm!(#global_asm);
>> >
>> > + #[cfg(not(MODULE))]
>> > + #[used(compiler)]
>> > + #[link_section = ".init.rodata"]
>> > + static #ident_modname_str: [u8; #name_len] =
>> > *#name_cstr.to_bytes_with_nul();
>>
>> [Severity: Low]
>> Will this cause a compilation failure for built-in Rust modules?
>>
>> It attempts to initialize a fixed-size array by dereferencing a dynamically
>> sized slice returned by to_bytes_with_nul(). This could break the build when
>> CONFIG_MODULES=n or when a Rust module is configured as built-in.
>
> Hi Gary,
>
> Calling .to_bytes_with_nul() on &CStr returns a slice reference (&[u8]), so
> dereferencing it yields an unsized slice ([u8]).
>
> To resolve this, we can follow the pattern already used in
> rust/macros/module.rs for emitting '.modinfo' entries construct a byte
> string literal at macro-expansion time using Literal::byte_string(). In
> Rust, a byte string literal (b"...\0") has type &'static [u8; N], which can
> be cleanly dereferenced with '*' into a fixed-size array [u8; N].
>
> Would the following be appropriate?
Looks reasonable.
Best,
Gary
>
> diff --git a/rust/macros/module.rs b/rust/macros/module.rs
> index a96157598197..67e3df8d4389 100644
> --- a/rust/macros/module.rs
> +++ b/rust/macros/module.rs
> @@ -493,7 +493,9 @@ pub(crate) fn module(info: ModuleInfo) ->
> Result<TokenStream> {
> );
>
> let name_cstr = CString::new(name.value()).expect("name contains
> NUL-terminator");
> - let name_len = name_cstr.to_bytes_with_nul().len();
> + let name_bytes = name_cstr.to_bytes_with_nul();
> + let name_len = name_bytes.len();
> + let name_byte_literal = Literal::byte_string(name_bytes);
>
> Ok(quote! {
> /// The module name.
> @@ -596,7 +598,7 @@ pub extern "C" fn cleanup_module() {
> #[cfg(not(MODULE))]
> #[used(compiler)]
> #[link_section = ".init.rodata"]
> - static #ident_modname_str: [u8; #name_len] =
> *#name_cstr.to_bytes_with_nul();
> + static #ident_modname_str: [u8; #name_len] =
> *#name_byte_literal;
>
> #[cfg(not(MODULE))]
> #[used(compiler)]
>
>
> Kind regards,
