linux-kernel - Re: [PATCH v2 3/9] x86/cfi: Document the "cfi=" bootparam options

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Message-ID: <20250904183254.GB2110053@ax162>
Date: Thu, 4 Sep 2025 11:32:54 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Kees Cook <kees@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Jonathan Corbet <corbet@....net>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>, linux-doc@...r.kernel.org,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Jeff Johnson <jeff.johnson@....qualcomm.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Marco Elver <elver@...gle.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Ramon de C Valle <rcvalle@...gle.com>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, linux-kbuild@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 3/9] x86/cfi: Document the "cfi=" bootparam options

On Wed, Sep 03, 2025 at 08:46:42PM -0700, Kees Cook wrote:
> The kernel-parameters.txt didn't have a section for the cfi= options.
> Add it.
> 
> Signed-off-by: Kees Cook <kees@...nel.org>
> ---

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

> ---
>  Documentation/admin-guide/kernel-parameters.txt | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 747a55abf494..8bbffbb334ab 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -608,6 +608,23 @@
>  	ccw_timeout_log	[S390]
>  			See Documentation/arch/s390/common_io.rst for details.
>  
> +	cfi=		[X86-64] Set Control Flow Integrity checking features
> +			when CONFIG_FINEIBT is enabled.
> +			Format: feature[,feature...]
> +			Default: auto
> +
> +			auto:	  Use FineIBT if IBT available, otherwise kCFI.
> +				  Under FineIBT, enable "paranoid" mode when
> +				  FRED is not available.
> +			off:	  Turn off CFI checking.
> +			kcfi:	  Use kCFI (disable FineIBT).
> +			fineibt:  Use FineIBT (even if IBT not available).
> +			norand:   Do not re-randomize CFI hashes.
> +			paranoid: Add caller hash checking under FineIBT.
> +			bhi:	  Enable register poisoning to stop speculation
> +				  across FineIBT. (Disabled by default.)
> +			warn:	  Do not enforce CFI checking: warn only.
> +
>  	cgroup_disable=	[KNL] Disable a particular controller or optional feature
>  			Format: {name of the controller(s) or feature(s) to disable}
>  			The effects of cgroup_disable=foo are:
> -- 
> 2.34.1
>