linux-kernel - Re: [PATCH 3/3] Revert "hardening: Disable GCC randstruct for COMPILE

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Message-ID: <202505301234.4F2C365F@keescook>
Date: Fri, 30 May 2025 12:37:06 -0700
From: Kees Cook <kees@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Thiago Jung Bauermann <thiago.bauermann@...aro.org>,
	akpm@...ux-foundation.org, arnd@...db.de, broonie@...nel.org,
	davidgow@...gle.com, diego.daniel.professional@...il.com,
	gnoack@...gle.com, gustavoars@...nel.org, jmorris@...ei.org,
	justinstitt@...gle.com, linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org,
	linux@...blig.org, llvm@...ts.linux.dev, mcgrof@...nel.org,
	mic@...ikod.net, morbo@...gle.com, nick.desaulniers+lkml@...il.com,
	paul@...l-moore.com, pmladek@...e.com, rmoar@...gle.com,
	serge@...lyn.com, tamird@...il.com, wangyuli@...ontech.com
Subject: Re: [PATCH 3/3] Revert "hardening: Disable GCC randstruct for
 COMPILE_TEST"

On Fri, May 30, 2025 at 12:09:04PM -0700, Nathan Chancellor wrote:
> On Thu, May 29, 2025 at 10:12:22PM -0700, Kees Cook wrote:
> > On Thu, May 29, 2025 at 09:06:46PM -0300, Thiago Jung Bauermann wrote:
> > > This commit was reported by our CI as breaking the allmodconfig build for
> > > the arm and arm64 architectures when using GCC 15. This is due to
> > > https://github.com/KSPP/linux/issues/367 :
> > > 
> > > 00:05:08 arch/arm64/kernel/kexec_image.c:132:14: internal compiler error: in comptypes_check_enum_int, at c/c-typeck.cc:1519
> > > 00:05:08   132 | const struct kexec_file_ops kexec_image_ops = {
> > > 00:05:08       |              ^~~~~~~~~~~~~~
> > 
> > I'm not able to reproduce this. Which specific version of GCC 15 and
> > on what distro are you seeing this?
> 
> It looks like this was also reported to Debian (I originally noticed it
> in the #gcc channel on OFTC a couple of weeks ago but forgot to mention
> it):
> 
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1104745
> 
> It looks like the difference might be whether GCC was built with
> additional checks or not based on the last couple of comments in that
> bug.

Ah, thanks for the additional pointer! Yeah, discussion has continued
on https://github.com/KSPP/linux/issues/367 which shows it's a problem
for GCC builds configured with "--enable-checking=yes"

It seems like this check is overly strict? I'm building GCC now to see
which aspect of the plugin is tripping it... I assume its decl
finalization, but we'll see.

-- 
Kees Cook