x86/bugs: Clarify that syscall hardening isn't a BHI mitigation

While syscall hardening helps prevent some BHI attacks, there's still
other low-hanging fruit remaining.  Don't classify it as a mitigation
and make it clear that the system may still be vulnerable if it doesn't
have a HW or SW mitigation enabled.

Fixes: ec9404e40e8f ("x86/bhi: Add BHI mitigation knob")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/b5951dae3fdee7f1520d5136a27be3bdfe95f88b.1712813475.git.jpoimboe@kernel.org

diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst
index 3cf18e4a1d9ab294cdb69683631d915cc3a3007c..5a39acf824835dc7ca748898881938a0a9c8d9cf 100644 (file)
--- a/Documentation/admin-guide/hw-vuln/spectre.rst
+++ b/Documentation/admin-guide/hw-vuln/spectre.rst
@@ -441,10 +441,10 @@ The possible values in this file are:
    - System is protected by BHI_DIS_S
  * - 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
-   - System is protected from userspace attacks by syscall hardening; KVM is protected by software clearing sequence
+ * - BHI: Vulnerable
+   - System is vulnerable to BHI
+ * - BHI: Vulnerable, KVM: SW loop
+   - System is vulnerable; KVM is protected by software clearing sequence
 
 Full mitigation might require a microcode update from the CPU
 vendor. When the necessary microcode is not available, the kernel will
@@ -661,8 +661,7 @@ kernel command line.
        spectre_bhi=
 
                [X86] Control mitigation of Branch History Injection
-               (BHI) vulnerability. Syscalls are hardened against BHI
-               regardless of this setting. This setting affects the deployment
+               (BHI) vulnerability.  This setting affects the deployment
                of the HW BHI control and the SW BHB clearing sequence.
 
                on

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a029ad6c4963c325a672d8e5b4c86b81c16112fd..a3874cc97892d949751e68418dcc09a53d39920e 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6065,8 +6065,7 @@
                        See Documentation/admin-guide/laptops/sonypi.rst
 
        spectre_bhi=    [X86] Control mitigation of Branch History Injection
-                       (BHI) vulnerability. Syscalls are hardened against BHI
-                       reglardless of this setting. This setting affects the
+                       (BHI) vulnerability.  This setting affects the
                        deployment of the HW BHI control and the SW BHB
                        clearing sequence.
 

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 08dfb94fcb3a41a0a390de383d94944cc0c0517b..9eeb60f5fbb356c187ade220c88b3e2768a7257c 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2818,10 +2818,10 @@ static const char *spectre_bhi_state(void)
                return "; BHI: SW loop, KVM: SW loop";
        else if (boot_cpu_has(X86_FEATURE_RETPOLINE) && rrsba_disabled)
                return "; BHI: Retpoline";
-       else if  (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
-               return "; BHI: Syscall hardening, KVM: SW loop";
+       else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
+               return "; BHI: Vulnerable, KVM: SW loop";
 
-       return "; BHI: Vulnerable (Syscall hardening enabled)";
+       return "; BHI: Vulnerable";
 }
 
 static ssize_t spectre_v2_show_state(char *buf)