[tip: x86/core] x86/cfi: Document the "cfi=" bootparam options

[tip: x86/core] x86/cfi: Document the "cfi=" bootparam options

[tip-bot2 for Kees Cook]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     24452d9ef17502965021ce5df30f4e184245a5ac
Gitweb:        https://git.kernel.org/tip/24452d9ef17502965021ce5df30f4e184245a5ac
Author:        Kees Cook <kees@kernel.org>
AuthorDate:    Wed, 03 Sep 2025 20:46:42 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 04 Sep 2025 21:59:08 +02:00

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@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20250904034656.3670313-3-kees@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 747a55a..8bbffbb 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: