[PATCH 6.8 152/172] x86/bugs: Fix BHI documentation

Greg Kroah-Hartman
2024-04-15T14:31:08Z

From: Josh Poimboeuf <jpoimboe@kernel.org>

commit dfe648903f42296866d79f10d03f8c85c9dfba30 upstream.

Fix up some inaccuracies in the BHI documentation.

Fixes: ec9404e40e8f ("x86/bhi: Add BHI mitigation knob")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/8c84f7451bfe0dd08543c6082a383f390d4aa7e2.1712813475.git.jpoimboe@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Documentation/admin-guide/hw-vuln/spectre.rst | 15 ++++++++-------
Documentation/admin-guide/kernel-parameters.txt | 12 +++++++-----
2 files changed, 15 insertions(+), 12 deletions(-)

--- 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
@@ -666,13 +666,14 @@ kernel command line.
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

--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3419,6 +3419,7 @@
reg_file_data_sampling=off [X86]
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]
@@ -6037,11 +6038,12 @@
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.