Re: [PATCH v2 0/3] module: Add compile-time check for embedded NUL characters

[Andy Shevchenko]

On Wed, Nov 05, 2025 at 02:03:59PM +0100, Daniel Gomez wrote:
> On 10/10/2025 05.06, Kees Cook wrote:
> >  v2:
> >  - use static_assert instead of _Static_assert
> >  - add Hans's Reviewed-by's
> >  v1: https://lore.kernel.org/lkml/20251008033844.work.801-kees@xxxxxxxxxx/
> > 
> > Hi!
> > 
> > A long time ago we had an issue with embedded NUL bytes in MODULE_INFO
> > strings[1]. While this stands out pretty strongly when you look at the
> > code, and we can't do anything about a binary module that just plain lies,
> > we never actually implemented the trivial compile-time check needed to
> > detect it.
> > 
> > Add this check (and fix 2 instances of needless trailing semicolons that
> > this change exposed).
> > 
> > Note that these patches were produced as part of another LLM exercise.
> > This time I wanted to try "what happens if I ask an LLM to go read
> > a specific LWN article and write a patch based on a discussion?" It
> > pretty effortlessly chose and implemented a suggested solution, tested
> > the change, and fixed new build warnings in the process.
> > 
> > Since this was a relatively short session, here's an overview of the
> > prompts involved as I guided it through a clean change and tried to see
> > how it would reason about static_assert vs _Static_assert. (It wanted
> > to use what was most common, not what was the current style -- we may
> > want to update the comment above the static_assert macro to suggest
> > using _Static_assert directly these days...)
> > 
> >   I want to fix a weakness in the module info strings. Read about it
> >   here: https://lwn.net/Articles/82305/
> > 
> >   Since it's only "info" that we need to check, can you reduce the checks
> >   to just that instead of all the other stuff?
> > 
> >   I think the change to the comment is redundent, and that should be
> >   in a commit log instead. Let's just keep the change to the static assert.
> > 
> >   Is "static_assert" the idiomatic way to use a static assert in this
> >   code base? I've seen _Static_assert used sometimes.
> > 
> >   What's the difference between the two?
> > 
> >   Does Linux use C11 by default now?
> > 
> >   Then let's not use the wrapper any more.
> > 
> >   Do an "allmodconfig all -s" build to verify this works for all modules
> >   in the kernel.
> > 
> > 
> > Thanks!
> > 
> > -Kees
> > 
> > [1] https://lwn.net/Articles/82305/
> > 
> > Kees Cook (3):
> >   media: dvb-usb-v2: lmedm04: Fix firmware macro definitions
> >   media: radio: si470x: Fix DRIVER_AUTHOR macro definition
> >   module: Add compile-time check for embedded NUL characters
> > 
> >  include/linux/moduleparam.h                   |  3 +++
> >  drivers/media/radio/si470x/radio-si470x-i2c.c |  2 +-
> >  drivers/media/usb/dvb-usb-v2/lmedm04.c        | 12 ++++++------
> >  3 files changed, 10 insertions(+), 7 deletions(-)
> > 
> 
> Reviewed-by: Daniel Gomez <da.gomez@xxxxxxxxxxx>
> 
> I have also tested a build of v6.18-rc3 + patches using allmodconfig:
> 
> Tested-by: Daniel Gomez <da.gomez@xxxxxxxxxxx>

Folks, are you aware that this change blown up the sparse?
Now there is a "bad constant expression" to each MODULE_*() macro line.

Nice that Uwe is in the Cc list, so IIRC he is Debian maintainer for sparse
and perhaps has an influence to it to some extent.

-- 
With Best Regards,
Andy Shevchenko