linux-hardening - Re: [PATCH] hardening: Refresh KCFI options, add some more

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Date: Tue, 30 Apr 2024 08:12:56 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-hardening@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hardening: Refresh KCFI options, add some more

On Mon, Apr 29, 2024 at 10:35:03PM -0700, Kees Cook wrote:
> On Mon, Apr 29, 2024 at 03:16:50PM -0700, Nathan Chancellor wrote:
> > On Fri, Apr 26, 2024 at 03:29:44PM -0700, Kees Cook wrote:
> > [...]
> > > +# Enable Kernel Control Flow Integrity (currently Clang only).
> > > +CONFIG_CFI_CLANG=y
> > > +# CONFIG_CFI_PERMISSIVE is not set
> > 
> > Should this be a part of kernel/configs/hardening.config because RISC-V
> > supports it (and 32-bit ARM will soon too)?
> 
> Probably yes. I was worried it might be "noisy" for archs that don't
> support it, but frankly if someone is using "make hardening.config" they
> probably want to know about unsupported options. :)

It would be potentially noisy as it is currently written since someone
building with GCC for arm64 or x86_64 could merge hardening.config into
their configuration and they would see CONFIG_CFI_CLANG get enabled by
merge_config.sh but on oldconfig or olddefconfig, it would get flipped
off again because the toolchain dependencies are not met. Might as well
make it architecture agnostic at that point :)

Cheers,
Nathan