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

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Message-ID: <aThqcq0iGge1pQCr@agluck-desk3>
Date: Tue, 9 Dec 2025 10:29:06 -0800
From: "Luck, Tony" <tony.luck@...el.com>
To: Daniel Gomez <da.gomez@...nel.org>, Eric Biggers <ebiggers@...nel.org>
CC: Kees Cook <kees@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, "Rusty
 Russell" <rusty@...tcorp.com.au>, Petr Pavlu <petr.pavlu@...e.com>, "Sami
 Tolvanen" <samitolvanen@...gle.com>, "linux-modules@...r.kernel.org"
	<linux-modules@...r.kernel.org>, Malcolm Priestley <tvboxspy@...il.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil
	<hverkuil@...nel.org>, Uwe Kleine-König
	<u.kleine-koenig@...gutronix.de>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-media@...r.kernel.org"
	<linux-media@...r.kernel.org>, "linux-hardening@...r.kernel.org"
	<linux-hardening@...r.kernel.org>
Subject: Re: [PATCH 3/3] module: Add compile-time check for embedded NUL
 characters

On Tue, Dec 09, 2025 at 08:45:14AM -0800, Luck, Tony wrote:
> On Tue, Dec 09, 2025 at 04:20:06PM +0000, Luck, Tony wrote:
> > >> Likewise, I just got the following kernel test robot report sent to me,
> > >> where it's warning about MODULE_LICENSE("GPL"):
> > >> https://lore.kernel.org/all/202512090359.7BkUaiC9-lkp@intel.com/
> > >
> > > Can you both confirm which version of sparse are you using?
> > >
> > > My understanding was that this patch fixed that problem:
> > > >https://lore.kernel.org/linux-sparse/CACePvbVG2KrGQq4cNKV=wbO5h=jp3M0RO1SdfX8kV4OukjPG8A@mail.gmail.com/T/#mf838b3e2e3245d88c30a801ea7473d5a5c0eb121
> > 
> > > The patch is already merged into the sparse tree, and I was not able to
> > > reproduce the issue.
> > 
> > I pulled the latest sparse source and re-checked before reporting. Top commit I have is the one you mention:
> > 
> > fbdde3127b83 ("builtin: implement __builtin_strlen() for constants")
> > 
> > I'm building latest Linus tree from the current merge window (well latest as-of yesterday):
> > 
> > c2f2b01b74be ("Merge tag 'i3c/for-6.19' of git://git.kernel.org/pub/scm/linux/kernel/git/i3c/linux")
> 
> I added a debug trace to the new expand_strlen() function added to
> sparse. It is being called and doing the right thing. My trace says:
> 
> 	len(GPL) = 3

Simple test case:

$ cat -n s.c
     1
     2  _Static_assert(sizeof("GPL") - 1 == 3, "sizeof");
     3
     4  _Static_assert(__builtin_strlen("GPL") == 3, "strlen");

$ sparse s.c
s.c:4:40: error: bad integer constant expression
s.c:4:40: error: static assertion failed: "strlen"

So the "sizeof" bit is OK. But the __builtin_strlen() isn't.

-Tony