[RFC PATCH v2 01/11] x86/msr-index: Add bit definitions for BHI_DIS_S and BHI_NO

[Chao Gao]

From: Zhang Chen <chen.zhang@xxxxxxxxx>

To ensure VM migration from a system where software mitigation works to
a system where it doesn't won't harm guest's security level, KVM must
mitigate BHI attacks for guests since migration is transparent to guests
and guests won't and can't react to VM migration.

For example, simple BHB clear sequence [1] is effective in mitigating BHI
attacks on processors prior to Alder Lake, but it is not on Alder Lake.
Guests migrated from prior to Alder Lake host to Alder Lake host become
vulnerable to BHI attacks even if the simmple BHB clear sequence is
deployed. In this case, KVM can enable hardware mitigation for guests by
setting BHI_DIS_S bit of IA32_SPEC_CTRL MSR.

Define the SPEC_CTRL_BHI_DIS_S of IA32_SPEC_CTRL MSR and BHI_NO bits in
arch_capabilities, which will be used by KVM later.

[1]: https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/branch-history-injection.html#inpage-nav-2-4

Signed-off-by: Zhang Chen <chen.zhang@xxxxxxxxx>
Co-developed-by: Chao Gao <chao.gao@xxxxxxxxx>
Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
Tested-by: Jiaan Lu <jiaan.lu@xxxxxxxxx>
---
 arch/x86/include/asm/msr-index.h       | 8 +++++++-
 tools/arch/x86/include/asm/msr-index.h | 8 +++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index ad35355ee43e..60b25d87b82c 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -48,8 +48,10 @@
 #define SPEC_CTRL_STIBP			BIT(SPEC_CTRL_STIBP_SHIFT)	/* STIBP mask */
 #define SPEC_CTRL_SSBD_SHIFT		2	   /* Speculative Store Bypass Disable bit */
 #define SPEC_CTRL_SSBD			BIT(SPEC_CTRL_SSBD_SHIFT)	/* Speculative Store Bypass Disable */
-#define SPEC_CTRL_RRSBA_DIS_S_SHIFT	6	   /* Disable RRSBA behavior */
+#define SPEC_CTRL_RRSBA_DIS_S_SHIFT	6	   /* Disable RRSBA behavior in supervisor mode */
 #define SPEC_CTRL_RRSBA_DIS_S		BIT(SPEC_CTRL_RRSBA_DIS_S_SHIFT)
+#define SPEC_CTRL_BHI_DIS_S_SHIFT	10	   /* Disable BHI behavior in supervisor mode */
+#define SPEC_CTRL_BHI_DIS_S		BIT(SPEC_CTRL_BHI_DIS_S_SHIFT)
 
 /* A mask for bits which the kernel toggles when controlling mitigations */
 #define SPEC_CTRL_MITIGATIONS_MASK	(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD \
@@ -151,6 +153,10 @@
 						 * are restricted to targets in
 						 * kernel.
 						 */
+#define ARCH_CAP_BHI_NO			BIT(20)	/*
+						 * Not susceptible to Branch History
+						 * Injection.
+						 */
 #define ARCH_CAP_PBRSB_NO		BIT(24)	/*
 						 * Not susceptible to Post-Barrier
 						 * Return Stack Buffer Predictions.
diff --git a/tools/arch/x86/include/asm/msr-index.h b/tools/arch/x86/include/asm/msr-index.h
index ad35355ee43e..6079a5fdb40b 100644
--- a/tools/arch/x86/include/asm/msr-index.h
+++ b/tools/arch/x86/include/asm/msr-index.h
@@ -48,8 +48,10 @@
 #define SPEC_CTRL_STIBP			BIT(SPEC_CTRL_STIBP_SHIFT)	/* STIBP mask */
 #define SPEC_CTRL_SSBD_SHIFT		2	   /* Speculative Store Bypass Disable bit */
 #define SPEC_CTRL_SSBD			BIT(SPEC_CTRL_SSBD_SHIFT)	/* Speculative Store Bypass Disable */
-#define SPEC_CTRL_RRSBA_DIS_S_SHIFT	6	   /* Disable RRSBA behavior */
+#define SPEC_CTRL_RRSBA_DIS_S_SHIFT	6	   /* Disable RRSBA behavior in supervisor mode */
 #define SPEC_CTRL_RRSBA_DIS_S		BIT(SPEC_CTRL_RRSBA_DIS_S_SHIFT)
+#define SPEC_CTRL_BHI_DIS_S_SHIFT	10         /* Disable BHI behavior in supervisor mode */
+#define SPEC_CTRL_BHI_DIS_S		BIT(SPEC_CTRL_BHI_DIS_S_SHIFT)
 
 /* A mask for bits which the kernel toggles when controlling mitigations */
 #define SPEC_CTRL_MITIGATIONS_MASK	(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD \
@@ -151,6 +153,10 @@
 						 * are restricted to targets in
 						 * kernel.
 						 */
+#define ARCH_CAP_BHI_NO			BIT(20) /*
+						 * Not susceptible to Branch History
+						 * Injection.
+						 */
 #define ARCH_CAP_PBRSB_NO		BIT(24)	/*
 						 * Not susceptible to Post-Barrier
 						 * Return Stack Buffer Predictions.
-- 
2.40.0