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

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Message-Id: <20250904034656.3670313-3-kees@kernel.org>
Date: Wed,  3 Sep 2025 20:46:42 -0700
From: Kees Cook <kees@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Kees Cook <kees@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	linux-doc@...r.kernel.org,
	Nathan Chancellor <nathan@...nel.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: [PATCH v2 3/9] x86/cfi: Document the "cfi=" bootparam options

The kernel-parameters.txt didn't have a section for the cfi= options.
Add it.

Signed-off-by: Kees Cook <kees@...nel.org>
---
Cc: Jonathan Corbet <corbet@....net>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: <linux-doc@...r.kernel.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