[PATCH 2/6] KVM: VMX: Add new ops in kvm_x86_ops for LASS violation check

[Zeng Guang]

Intel introduce LASS (Linear Address Separation) feature providing
an independent mechanism to achieve the mode-based protection.

LASS partitions 64-bit linear address space into two halves, user-mode
address (LA[bit 63]=0) and supervisor-mode address (LA[bit 63]=1). It
stops any code execution or data access
    1. from user mode to supervisor-mode address space
    2. from supervisor mode to user-mode address space
and generates LASS violation fault accordingly.

A supervisor mode data access causes a LASS violation only if supervisor
mode access protection is enabled (CR4.SMAP = 1) and either RFLAGS.AC = 0
or the access implicitly accesses a system data structure.

Following are the rule of LASS violation check on the linear address(LA).
User access to supervisor-mode address space:
    LA[bit 63] && (CPL == 3)
Supervisor access to user-mode address space:
    Instruction fetch: !LA[bit 63] && (CPL < 3)
    Data access: !LA[bit 63] && (CR4.SMAP==1) && ((RFLAGS.AC == 0 &&
		 CPL < 3) || Implicit supervisor access)

Add new ops in kvm_x86_ops to do LASS violation check.

Signed-off-by: Zeng Guang <guang.zeng@xxxxxxxxx>
---
 arch/x86/include/asm/kvm-x86-ops.h |  1 +
 arch/x86/include/asm/kvm_host.h    |  5 +++
 arch/x86/kvm/vmx/vmx.c             | 55 ++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/vmx.h             |  2 ++
 4 files changed, 63 insertions(+)

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index abccd51dcfca..f76c07f2674b 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -131,6 +131,7 @@ KVM_X86_OP(msr_filter_changed)
 KVM_X86_OP(complete_emulated_msr)
 KVM_X86_OP(vcpu_deliver_sipi_vector)
 KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
+KVM_X86_OP_OPTIONAL_RET0(check_lass);
 
 #undef KVM_X86_OP
 #undef KVM_X86_OP_OPTIONAL
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8ff89a52ef66..31fb8699a1ff 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -69,6 +69,9 @@
 #define KVM_X86_NOTIFY_VMEXIT_VALID_BITS	(KVM_X86_NOTIFY_VMEXIT_ENABLED | \
 						 KVM_X86_NOTIFY_VMEXIT_USER)
 
+/* x86-specific emulation flags */
+#define KVM_X86_EMULFLAG_SKIP_LASS	_BITULL(1)
+
 /* x86-specific vcpu->requests bit members */
 #define KVM_REQ_MIGRATE_TIMER		KVM_ARCH_REQ(0)
 #define KVM_REQ_REPORT_TPR_ACCESS	KVM_ARCH_REQ(1)
@@ -1706,6 +1709,8 @@ struct kvm_x86_ops {
 	 * Returns vCPU specific APICv inhibit reasons
 	 */
 	unsigned long (*vcpu_get_apicv_inhibit_reasons)(struct kvm_vcpu *vcpu);
+
+	bool (*check_lass)(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags);
 };
 
 struct kvm_x86_nested_ops {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c923d7599d71..581327ede66a 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8070,6 +8070,59 @@ static void vmx_vm_destroy(struct kvm *kvm)
 	free_pages((unsigned long)kvm_vmx->pid_table, vmx_get_pid_table_order(kvm));
 }
 
+/*
+ * Determine whether an access to the linear address causes a LASS violation.
+ * LASS protection is only effective in long mode. As a prerequisite, caller
+ * should make sure VM running in long mode and invoke this api to do LASS
+ * violation check.
+ */
+bool __vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags)
+{
+	bool user_mode, user_as, rflags_ac;
+
+	if (!!(flags & KVM_X86_EMULFLAG_SKIP_LASS) ||
+	    !kvm_is_cr4_bit_set(vcpu, X86_CR4_LASS))
+		return false;
+
+	WARN_ON_ONCE(!is_long_mode(vcpu));
+
+	user_as = !(la >> 63);
+
+	/*
+	 * An access is a supervisor-mode access if CPL < 3 or if it implicitly
+	 * accesses a system data structure. For implicit accesses to system
+	 * data structure, the processor acts as if RFLAGS.AC is clear.
+	 */
+	if (access & PFERR_IMPLICIT_ACCESS) {
+		user_mode = false;
+		rflags_ac = false;
+	} else {
+		user_mode = vmx_get_cpl(vcpu) == 3;
+		if (!user_mode)
+			rflags_ac = !!(kvm_get_rflags(vcpu) & X86_EFLAGS_AC);
+	}
+
+	if (user_mode != user_as) {
+		/*
+		 * Supervisor-mode _data_ accesses to user address space
+		 * cause LASS violations only if SMAP is enabled.
+		 */
+		if (!user_mode && !(access & PFERR_FETCH_MASK)) {
+			return kvm_is_cr4_bit_set(vcpu, X86_CR4_SMAP) &&
+			       !rflags_ac;
+		} else {
+			return true;
+		}
+	}
+
+	return false;
+}
+
+static bool vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags)
+{
+	return is_long_mode(vcpu) && __vmx_check_lass(vcpu, access, la, flags);
+}
+
 static struct kvm_x86_ops vmx_x86_ops __initdata = {
 	.name = "kvm_intel",
 
@@ -8207,6 +8260,8 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
 	.complete_emulated_msr = kvm_complete_insn_gp,
 
 	.vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector,
+
+	.check_lass = vmx_check_lass,
 };
 
 static unsigned int vmx_handle_intel_pt_intr(void)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index a3da84f4ea45..6569385a5978 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -433,6 +433,8 @@ void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, int type);
 u64 vmx_get_l2_tsc_offset(struct kvm_vcpu *vcpu);
 u64 vmx_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu);
 
+bool __vmx_check_lass(struct kvm_vcpu *vcpu, u64 access, u64 la, u64 flags);
+
 static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
 					     int type, bool value)
 {
-- 
2.27.0