The moduleparam code allows modules to provide their own definition of
MODULE_PARAM_PREFIX, instead of using the default KBUILD_MODNAME ".".

Commit 730b69d22525 ("module: check kernel param length at compile time,
not runtime") added a check to ensure the prefix doesn't exceed
MODULE_NAME_LEN, as this is what param_sysfs_builtin() expects.

Later, commit 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking
for sysfs perms.") removed this check, but there is no indication this was
intentional.

Since the check is still useful for param_sysfs_builtin() to function
properly, reintroduce it in __module_param_call(), but in a modernized form
using static_assert().

While here, clean up the __module_param_call() comments. In particular,
remove the comment "Default value instead of permissions?", which comes
from commit 9774a1f54f17 ("[PATCH] Compile-time check re world-writeable
module params"). This comment was related to the test variable
__param_perm_check_##name, which was removed in the previously mentioned
commit 58f86cc89c33.

Fixes: 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking for sysfs perms.")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
---
 include/linux/moduleparam.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index bfb85fd13e1f..110e9d09de24 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -282,10 +282,9 @@ struct kparam_array
 #define __moduleparam_const const
 #endif
 
-/* This is the fundamental function for registering boot/module
-   parameters. */
+/* This is the fundamental function for registering boot/module parameters. */
 #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
-	/* Default value instead of permissions? */			\
+	static_assert(sizeof(""prefix) - 1 <= MAX_PARAM_PREFIX_LEN);	\
 	static const char __param_str_##name[] = prefix #name;		\
 	static struct kernel_param __moduleparam_const __param_##name	\
 	__used __section("__param")					\
-- 
2.49.0

On 30/06/2025 16.32, Petr Pavlu wrote:
> The moduleparam code allows modules to provide their own definition of
> MODULE_PARAM_PREFIX, instead of using the default KBUILD_MODNAME ".".
> 
> Commit 730b69d22525 ("module: check kernel param length at compile time,
> not runtime") added a check to ensure the prefix doesn't exceed
> MODULE_NAME_LEN, as this is what param_sysfs_builtin() expects.
> 
> Later, commit 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking
> for sysfs perms.") removed this check, but there is no indication this was
> intentional.
> 
> Since the check is still useful for param_sysfs_builtin() to function
> properly, reintroduce it in __module_param_call(), but in a modernized form
> using static_assert().
> 
> While here, clean up the __module_param_call() comments. In particular,
> remove the comment "Default value instead of permissions?", which comes
> from commit 9774a1f54f17 ("[PATCH] Compile-time check re world-writeable
> module params"). This comment was related to the test variable
> __param_perm_check_##name, which was removed in the previously mentioned
> commit 58f86cc89c33.
> 
> Fixes: 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking for sysfs perms.")
> Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
> ---
>  include/linux/moduleparam.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
> index bfb85fd13e1f..110e9d09de24 100644
> --- a/include/linux/moduleparam.h
> +++ b/include/linux/moduleparam.h
> @@ -282,10 +282,9 @@ struct kparam_array
>  #define __moduleparam_const const
>  #endif
>  
> -/* This is the fundamental function for registering boot/module
> -   parameters. */
> +/* This is the fundamental function for registering boot/module parameters. */
>  #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
> -	/* Default value instead of permissions? */			\
> +	static_assert(sizeof(""prefix) - 1 <= MAX_PARAM_PREFIX_LEN);	\

Can you clarify if -1 to remove the dot from prefix?

Final code 
	static_assert(sizeof(""prefix) - 1 <= __MODULE_NAME_LEN);	\

with __MODULE_NAME_LEN being:

#define __MODULE_NAME_LEN (64 - sizeof(unsigned long))


>  	static const char __param_str_##name[] = prefix #name;		\
>  	static struct kernel_param __moduleparam_const __param_##name	\
>  	__used __section("__param")					\

On 7/17/25 9:23 PM, Daniel Gomez wrote:
> On 30/06/2025 16.32, Petr Pavlu wrote:
>> The moduleparam code allows modules to provide their own definition of
>> MODULE_PARAM_PREFIX, instead of using the default KBUILD_MODNAME ".".
>>
>> Commit 730b69d22525 ("module: check kernel param length at compile time,
>> not runtime") added a check to ensure the prefix doesn't exceed
>> MODULE_NAME_LEN, as this is what param_sysfs_builtin() expects.
>>
>> Later, commit 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking
>> for sysfs perms.") removed this check, but there is no indication this was
>> intentional.
>>
>> Since the check is still useful for param_sysfs_builtin() to function
>> properly, reintroduce it in __module_param_call(), but in a modernized form
>> using static_assert().
>>
>> While here, clean up the __module_param_call() comments. In particular,
>> remove the comment "Default value instead of permissions?", which comes
>> from commit 9774a1f54f17 ("[PATCH] Compile-time check re world-writeable
>> module params"). This comment was related to the test variable
>> __param_perm_check_##name, which was removed in the previously mentioned
>> commit 58f86cc89c33.
>>
>> Fixes: 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking for sysfs perms.")
>> Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
>> ---
>>  include/linux/moduleparam.h | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
>> index bfb85fd13e1f..110e9d09de24 100644
>> --- a/include/linux/moduleparam.h
>> +++ b/include/linux/moduleparam.h
>> @@ -282,10 +282,9 @@ struct kparam_array
>>  #define __moduleparam_const const
>>  #endif
>>  
>> -/* This is the fundamental function for registering boot/module
>> -   parameters. */
>> +/* This is the fundamental function for registering boot/module parameters. */
>>  #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
>> -	/* Default value instead of permissions? */			\
>> +	static_assert(sizeof(""prefix) - 1 <= MAX_PARAM_PREFIX_LEN);	\
> 
> Can you clarify if -1 to remove the dot from prefix?
> 
> Final code 
> 	static_assert(sizeof(""prefix) - 1 <= __MODULE_NAME_LEN);	\
> 
> with __MODULE_NAME_LEN being:
> 
> #define __MODULE_NAME_LEN (64 - sizeof(unsigned long))

Correct, -1 is to account for the dot at the end of the prefix.

I actually also wanted to assert that the prefix ends with a dot, but
unfortunately prefix[sizeof(prefix)-2] (with prefix being a string
literal) is not a constant expression in C.

-- 
Thanks,
Petr

On 21/07/2025 11.21, Petr Pavlu wrote:
> On 7/17/25 9:23 PM, Daniel Gomez wrote:
>> On 30/06/2025 16.32, Petr Pavlu wrote:
>>> The moduleparam code allows modules to provide their own definition of
>>> MODULE_PARAM_PREFIX, instead of using the default KBUILD_MODNAME ".".
>>>
>>> Commit 730b69d22525 ("module: check kernel param length at compile time,
>>> not runtime") added a check to ensure the prefix doesn't exceed
>>> MODULE_NAME_LEN, as this is what param_sysfs_builtin() expects.
>>>
>>> Later, commit 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking
>>> for sysfs perms.") removed this check, but there is no indication this was
>>> intentional.
>>>
>>> Since the check is still useful for param_sysfs_builtin() to function
>>> properly, reintroduce it in __module_param_call(), but in a modernized form
>>> using static_assert().
>>>
>>> While here, clean up the __module_param_call() comments. In particular,
>>> remove the comment "Default value instead of permissions?", which comes
>>> from commit 9774a1f54f17 ("[PATCH] Compile-time check re world-writeable
>>> module params"). This comment was related to the test variable
>>> __param_perm_check_##name, which was removed in the previously mentioned
>>> commit 58f86cc89c33.
>>>
>>> Fixes: 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking for sysfs perms.")
>>> Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
>>> ---
>>>  include/linux/moduleparam.h | 5 ++---
>>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
>>> index bfb85fd13e1f..110e9d09de24 100644
>>> --- a/include/linux/moduleparam.h
>>> +++ b/include/linux/moduleparam.h
>>> @@ -282,10 +282,9 @@ struct kparam_array
>>>  #define __moduleparam_const const
>>>  #endif
>>>  
>>> -/* This is the fundamental function for registering boot/module
>>> -   parameters. */
>>> +/* This is the fundamental function for registering boot/module parameters. */
>>>  #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
>>> -	/* Default value instead of permissions? */			\
>>> +	static_assert(sizeof(""prefix) - 1 <= MAX_PARAM_PREFIX_LEN);	\
>>
>> Can you clarify if -1 to remove the dot from prefix?
>>
>> Final code 
>> 	static_assert(sizeof(""prefix) - 1 <= __MODULE_NAME_LEN);	\
>>
>> with __MODULE_NAME_LEN being:
>>
>> #define __MODULE_NAME_LEN (64 - sizeof(unsigned long))
> 
> Correct, -1 is to account for the dot at the end of the prefix.

LGTM,

Reviewed-by: Daniel Gomez <da.gomez@samsung.com>

> 
> I actually also wanted to assert that the prefix ends with a dot, but
> unfortunately prefix[sizeof(prefix)-2] (with prefix being a string
> literal) is not a constant expression in C.
> 

But even if that would be possible, there are some calls that do not have
a prefix with dot. For example,

#define core_param(name, var, type, perm)				\
	param_check_##type(name, &(var));				\
	__module_param_call("", name, &param_ops_##type, &var, perm, -1, 0)

So, you'd have to handle both cases. I mean, where __module_param_call(<prefix>
is used with either MODULE_PARAM_PREFIX or an empty string "".