[PATCH] KVM: x86/pmu: Don't expose guest LBR if the LBR_SELECT is shared per physical core

[Like Xu]

From: Like Xu <likexu@xxxxxxxxxxx>

According to Intel SDM, the Last Branch Record Filtering Select Register
(R/W) is defined as shared per physical core rather than per logical core
on some older Intel platforms: Silvermont, Airmont, Goldmont and Nehalem.

To avoid LBR attacks or accidental data leakage, on these specific
platforms, KVM should not expose guest LBR capability even if HT is
disabled on the host, considering that the HT state can be dynamically
changed, yet the KVM capabilities are initialized at module initialisation.

Fixes: be635e34c284 ("KVM: vmx/pmu: Expose LBR_FMT in the MSR_IA32_PERF_CAPABILITIES")
Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
---
 arch/x86/include/asm/intel-family.h |  1 +
 arch/x86/kvm/vmx/capabilities.h     | 19 ++++++++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/intel-family.h b/arch/x86/include/asm/intel-family.h
index 27158436f322..f35c915566e3 100644
--- a/arch/x86/include/asm/intel-family.h
+++ b/arch/x86/include/asm/intel-family.h
@@ -119,6 +119,7 @@
 
 #define INTEL_FAM6_ATOM_SILVERMONT	0x37 /* Bay Trail, Valleyview */
 #define INTEL_FAM6_ATOM_SILVERMONT_D	0x4D /* Avaton, Rangely */
+#define INTEL_FAM6_ATOM_SILVERMONT_X3	0x5D /* X3-C3000 based on Silvermont */
 #define INTEL_FAM6_ATOM_SILVERMONT_MID	0x4A /* Merriefield */
 
 #define INTEL_FAM6_ATOM_AIRMONT		0x4C /* Cherry Trail, Braswell */
diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 4705ad55abb5..ff9596d7112d 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -3,6 +3,7 @@
 #define __KVM_X86_VMX_CAPS_H
 
 #include <asm/vmx.h>
+#include <asm/cpu_device_id.h>
 
 #include "lapic.h"
 
@@ -376,6 +377,21 @@ static inline bool vmx_pt_mode_is_host_guest(void)
 	return pt_mode == PT_MODE_HOST_GUEST;
 }
 
+static const struct x86_cpu_id lbr_select_shared_cpu[] = {
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_SILVERMONT, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_SILVERMONT_MID, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_SILVERMONT_D, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_SILVERMONT_X3, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_AIRMONT_MID, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_GOLDMONT, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(ATOM_GOLDMONT_PLUS, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(NEHALEM_EP, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(NEHALEM, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(NEHALEM_G, NULL),
+	X86_MATCH_INTEL_FAM6_MODEL(NEHALEM_EX, NULL),
+	{}
+};
+
 static inline u64 vmx_get_perf_capabilities(void)
 {
 	u64 perf_cap = 0;
@@ -383,7 +399,8 @@ static inline u64 vmx_get_perf_capabilities(void)
 	if (boot_cpu_has(X86_FEATURE_PDCM))
 		rdmsrl(MSR_IA32_PERF_CAPABILITIES, perf_cap);
 
-	perf_cap &= PMU_CAP_LBR_FMT;
+	if (!x86_match_cpu(lbr_select_shared_cpu))
+		perf_cap &= PMU_CAP_LBR_FMT;
 
 	/*
 	 * Since counters are virtualized, KVM would support full
-- 
2.32.0