[PATCH 10/15] x86/bugs: Fix BHI documentation

[Yuxuan Luo]

From: Josh Poimboeuf <jpoimboe at kernel.org>

Fix up some inaccuracies in the BHI documentation.

Fixes: ec9404e40e8f ("x86/bhi: Add BHI mitigation knob")
Signed-off-by: Josh Poimboeuf <jpoimboe at kernel.org>
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Reviewed-by: Nikolay Borisov <nik.borisov at suse.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Sean Christopherson <seanjc at google.com>
Link: https://lore.kernel.org/r/8c84f7451bfe0dd08543c6082a383f390d4aa7e2.1712813475.git.jpoimboe@kernel.org
(cherry picked from commit dfe648903f42296866d79f10d03f8c85c9dfba30)
CVE-2024-2201
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 Documentation/admin-guide/hw-vuln/spectre.rst   | 15 ++++++++-------
 Documentation/admin-guide/kernel-parameters.txt | 12 +++++++-----
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst
index 8e003eb6ac0fd..fe50e9cb00282 100644
--- a/Documentation/admin-guide/hw-vuln/spectre.rst
+++ b/Documentation/admin-guide/hw-vuln/spectre.rst
@@ -439,11 +439,11 @@ The possible values in this file are:
    - System is protected by retpoline
  * - BHI: BHI_DIS_S
    - System is protected by BHI_DIS_S
- * - BHI: SW loop; KVM SW loop
+ * - BHI: SW loop, KVM SW loop
    - System is protected by software clearing sequence
  * - BHI: Syscall hardening
    - Syscalls are hardened against BHI
- * - BHI: Syscall hardening; KVM: SW loop
+ * - BHI: Syscall hardening, KVM: SW loop
    - System is protected from userspace attacks by syscall hardening; KVM is protected by software clearing sequence
 
 Full mitigation might require a microcode update from the CPU
@@ -708,13 +708,14 @@ For user space mitigation:
 		of the HW BHI control and the SW BHB clearing sequence.
 
 		on
-			unconditionally enable.
+			(default) Enable the HW or SW mitigation as
+			needed.
 		off
-			unconditionally disable.
+			Disable the mitigation.
 		auto
-			enable if hardware mitigation
-			control(BHI_DIS_S) is available, otherwise
-			enable alternate mitigation in KVM.
+			Enable the HW mitigation if needed, but
+			*don't* enable the SW mitigation except for KVM.
+			The system may be vulnerable.
 
 For spectre_v2_user see Documentation/admin-guide/kernel-parameters.txt
 
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9b38050fdf5f0..bccf22d167622 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2748,6 +2748,7 @@
 					       nospectre_v2 [X86,PPC,S390,ARM64]
 					       retbleed=off [X86]
 					       spec_store_bypass_disable=off [X86,PPC]
+					       spectre_bhi=off [X86]
 					       spectre_v2_user=off [X86]
 					       srbds=off [X86,INTEL]
 					       ssbd=force-off [ARM64]
@@ -4611,11 +4612,12 @@
 			deployment of the HW BHI control and the SW BHB
 			clearing sequence.
 
-			on   - unconditionally enable.
-			off  - unconditionally disable.
-			auto - (default) enable hardware mitigation
-			       (BHI_DIS_S) if available, otherwise enable
-			       alternate mitigation in KVM.
+			on   - (default) Enable the HW or SW mitigation
+			       as needed.
+			off  - Disable the mitigation.
+			auto - Enable the HW mitigation if needed, but
+			       *don't* enable the SW mitigation except
+			       for KVM.  The system may be vulnerable.
 
 	spectre_v2=	[X86] Control mitigation of Spectre variant 2
 			(indirect branch speculation) vulnerability.
-- 
2.34.1