linux-kernel - Re: [PATCH] [RFC] xfrm: work around a clang-19 fortifiy-string false-positive

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Date: Fri, 12 Apr 2024 14:21:36 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...nel.org>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Leon Romanovsky <leon@...nel.org>, Lin Ma <linma@....edu.cn>,
	Simon Horman <horms@...nel.org>, Breno Leitao <leitao@...ian.org>,
	Tobias Brunner <tobias@...ongswan.org>,
	Raed Salem <raeds@...dia.com>, Netdev <netdev@...r.kernel.org>,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] [RFC] xfrm: work around a clang-19 fortifiy-string
 false-positive

On Thu, Apr 11, 2024 at 01:35:05PM +0200, Arnd Bergmann wrote:
> On Wed, Apr 10, 2024, at 19:45, Nathan Chancellor wrote:
> 
> > Unfortunately, I have no idea why it is complaining nor why your patch
> > resolves it but the combination of FORTIFY_SOURCE and KASAN certainly
> > seems like a reasonable place to start looking. I will see if I can come
> > up with a smaller reproducer to see if it becomes more obvious why this
> > code triggers this warning.
> 
> I know at least why my patch avoids the warning -- it removes the
> call to memset() that contains the check.

Yeah duh... :/ I should have realized that before I sent that message
heh.

> Unfortunately that still doesn't explain what caused it.

Right, I'll see if I can cvise something out now that we have a more
isolated set of conditions. I guess the only question will be if I can
build a file preprocessed with CONFIG_KASAN=y will build with and
without '-fsanitize=kernel-address'...

Cheers,
Nathan