[PATCH 14/15] x86/bugs: Clarify that syscall hardening isn't a BHI mitigation

[Yuxuan Luo]

From: Josh Poimboeuf <jpoimboe at kernel.org>

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 at kernel.org>
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Sean Christopherson <seanjc at google.com>
Link: https://lore.kernel.org/r/b5951dae3fdee7f1520d5136a27be3bdfe95f88b.1712813475.git.jpoimboe@kernel.org
(cherry picked from commit 5f882f3b0a8bf0788d5a0ee44b1191de5319bb8a)
CVE-2024-2201
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 Documentation/admin-guide/hw-vuln/spectre.rst   | 11 +++++------
 Documentation/admin-guide/kernel-parameters.txt |  3 +--
 arch/x86/kernel/cpu/bugs.c                      |  6 +++---
 3 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst
index fe50e9cb00282..601be75541bf2 100644
--- 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
@@ -703,8 +703,7 @@ For user space mitigation:
 	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 bccf22d167622..59714ce57f3b1 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4607,8 +4607,7 @@
 			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 4cdf99c1feafd..fe27ebe95030a 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2356,10 +2356,10 @@ static const char * const 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)
-- 
2.34.1