[RFC PATCH 1/9] x86/speculation: Introduce Intel SPEC_CTRL BHI related definition

Zhang Chen
2022-12-10T16:19:01Z

Define BHI_NO bit and new control of BHI hardware mitigation in
IA32_SPEC_CTRL. These definitions are used by following KVM patches
to determine whether to enforce BHI hardware mitigiations for
guests transparently.

BHI_NO means the processor isn't vulnernable to BHI attacks. BHI_DIS_S
is a new indirect predictor control. Once enabled, BHI_DIS_S prevents
predicted targets of indirect branches executed in CPL0/1/2 from being
selected based on branch history from branches executed in CPL3.
While set in the VMX root, it also prevents predicted targets executed
in CPL0 from being selected based on branch history from branches
executed in a VMX non-root.

Branch History Injection (BHI) describes a specific form of intra-mode
BTI, where an attacker may manipulate branch history before transitioning
from user to supervisor mode (or from VMX non-root/guest to root mode)
in an effort to cause an indirect branch predictor to select a specific
predictor entry for an indirect branch, and a disclosure gadget at the
predicted target will transiently execute. This may be possible since
the relevant branch history may contain branches taken in previous
security contexts, and in particular, in other predictor modes.

Refer to below link for more information:
https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/branch-history-injection.html

Signed-off-by: Zhang Chen <chen.zhang@intel.com>
---
arch/x86/include/asm/msr-index.h | 6 ++++++
tools/arch/x86/include/asm/msr-index.h | 6 ++++++
2 files changed, 12 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 4a2af82553e4..1143ac9400c3 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -53,6 +53,8 @@
#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 BIT(SPEC_CTRL_RRSBA_DIS_S_SHIFT)
+#define SPEC_CTRL_BHI_DIS_S_SHIFT 10 /* Enable BHI_DIS_S behavior */
+#define SPEC_CTRL_BHI_DIS_S BIT(SPEC_CTRL_BHI_DIS_S_SHIFT)

#define MSR_IA32_PRED_CMD 0x00000049 /* Prediction Command */
#define PRED_CMD_IBPB BIT(0) /* Indirect Branch Prediction Barrier */
@@ -150,6 +152,10 @@
* 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 f17ade084720..aed18b76dee0 100644
--- a/tools/arch/x86/include/asm/msr-index.h
+++ b/tools/arch/x86/include/asm/msr-index.h
@@ -53,6 +53,8 @@
#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 BIT(SPEC_CTRL_RRSBA_DIS_S_SHIFT)
+#define SPEC_CTRL_BHI_DIS_S_SHIFT 10 /* Enable BHI_DIS_S behavior */
+#define SPEC_CTRL_BHI_DIS_S BIT(SPEC_CTRL_BHI_DIS_S_SHIFT)

#define MSR_IA32_PRED_CMD 0x00000049 /* Prediction Command */
#define PRED_CMD_IBPB BIT(0) /* Indirect Branch Prediction Barrier */
@@ -150,6 +152,10 @@
* 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.
--
2.25.1