[RFC PATCH 4/4] KVM: vmx: add support for emulating UMIP

[Paolo Bonzini <pbonzini@redhat.com>]

UMIP (User-Mode Instruction Prevention) is a feature of future
Intel processors (Cannonlake?) that blocks SLDT, SGDT, STR, SIDT
and SMSW from user-mode processes.

On Intel systems it's *almost* possible to emulate it; it slows
down the instructions when they're executed in ring 0, but they
are really never executed in practice.  The catch is that SMSW
doesn't cause a vmexit, and hence SMSW will not fault.

When UMIP is enabled but not supported by the host, descriptor table
exits are enabled, and the emulator takes care of injecting a #GP when
any of SLDT, SGDT, STR, SIDT are encountered.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/include/asm/vmx.h      |  1 +
 arch/x86/include/uapi/asm/vmx.h |  4 ++++
 arch/x86/kvm/vmx.c              | 36 ++++++++++++++++++++++++++++++++++--
 3 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 14c63c7e8337..8b95f0ec0190 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -60,6 +60,7 @@
  */
 #define SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES 0x00000001
 #define SECONDARY_EXEC_ENABLE_EPT               0x00000002
+#define SECONDARY_EXEC_DESC			0x00000004
 #define SECONDARY_EXEC_RDTSCP			0x00000008
 #define SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE   0x00000010
 #define SECONDARY_EXEC_ENABLE_VPID              0x00000020
diff --git a/arch/x86/include/uapi/asm/vmx.h b/arch/x86/include/uapi/asm/vmx.h
index 5b15d94a33f8..2f9a69b9559c 100644
--- a/arch/x86/include/uapi/asm/vmx.h
+++ b/arch/x86/include/uapi/asm/vmx.h
@@ -65,6 +65,8 @@
 #define EXIT_REASON_TPR_BELOW_THRESHOLD 43
 #define EXIT_REASON_APIC_ACCESS         44
 #define EXIT_REASON_EOI_INDUCED         45
+#define EXIT_REASON_GDTR_IDTR           46
+#define EXIT_REASON_LDTR_TR             47
 #define EXIT_REASON_EPT_VIOLATION       48
 #define EXIT_REASON_EPT_MISCONFIG       49
 #define EXIT_REASON_INVEPT              50
@@ -114,6 +116,8 @@
 	{ EXIT_REASON_MCE_DURING_VMENTRY,    "MCE_DURING_VMENTRY" }, \
 	{ EXIT_REASON_TPR_BELOW_THRESHOLD,   "TPR_BELOW_THRESHOLD" }, \
 	{ EXIT_REASON_APIC_ACCESS,           "APIC_ACCESS" }, \
+	{ EXIT_REASON_GDTR_IDTR,	     "GDTR_IDTR" }, \
+	{ EXIT_REASON_LDTR_TR,		     "LDTR_TR" }, \
 	{ EXIT_REASON_EPT_VIOLATION,         "EPT_VIOLATION" }, \
 	{ EXIT_REASON_EPT_MISCONFIG,         "EPT_MISCONFIG" }, \
 	{ EXIT_REASON_INVEPT,                "INVEPT" }, \
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b133fc3d6a7d..0706e363c5e3 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3342,6 +3342,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
 			SECONDARY_EXEC_ENABLE_EPT |
 			SECONDARY_EXEC_UNRESTRICTED_GUEST |
 			SECONDARY_EXEC_PAUSE_LOOP_EXITING |
+			SECONDARY_EXEC_DESC |
 			SECONDARY_EXEC_RDTSCP |
 			SECONDARY_EXEC_ENABLE_INVPCID |
 			SECONDARY_EXEC_APIC_REGISTER_VIRT |
@@ -3967,6 +3968,14 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 		(to_vmx(vcpu)->rmode.vm86_active ?
 		 KVM_RMODE_VM_CR4_ALWAYS_ON : KVM_PMODE_VM_CR4_ALWAYS_ON);
 
+	if ((cr4 & X86_CR4_UMIP) && !boot_cpu_has(X86_FEATURE_UMIP)) {
+		vmcs_set_bits(SECONDARY_VM_EXEC_CONTROL,
+			      SECONDARY_EXEC_DESC);
+		hw_cr4 &= ~X86_CR4_UMIP;
+	} else
+		vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,
+				SECONDARY_EXEC_DESC);
+
 	if (cr4 & X86_CR4_VMXE) {
 		/*
 		 * To use VMXON (and later other VMX instructions), a guest
@@ -4913,6 +4922,11 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx)
 static u32 vmx_secondary_exec_control(struct vcpu_vmx *vmx)
 {
 	u32 exec_control = vmcs_config.cpu_based_2nd_exec_ctrl;
+
+	/* SECONDARY_EXEC_DESC is enabled/disabled on writes to CR4.UMIP,
+	 * in vmx_set_cr4.  */
+	exec_control &= ~SECONDARY_EXEC_DESC;
+
 	if (!cpu_need_virtualize_apic_accesses(&vmx->vcpu))
 		exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
 	if (vmx->vpid == 0)
@@ -5649,6 +5663,12 @@ static void handle_clts(struct kvm_vcpu *vcpu)
 		vmx_set_cr0(vcpu, kvm_read_cr0_bits(vcpu, ~X86_CR0_TS));
 }
 
+static int handle_desc(struct kvm_vcpu *vcpu)
+{
+	WARN_ON(!(vcpu->arch.cr4 & X86_CR4_UMIP));
+	return emulate_instruction(vcpu, 0) == EMULATE_DONE;
+}
+
 static int handle_cr(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qualification, val;
@@ -7705,6 +7731,8 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[EXIT_REASON_XSETBV]                  = handle_xsetbv,
 	[EXIT_REASON_TASK_SWITCH]             = handle_task_switch,
 	[EXIT_REASON_MCE_DURING_VMENTRY]      = handle_machine_check,
+	[EXIT_REASON_GDTR_IDTR]		      = handle_desc,
+	[EXIT_REASON_LDTR_TR]		      = handle_desc,
 	[EXIT_REASON_EPT_VIOLATION]	      = handle_ept_violation,
 	[EXIT_REASON_EPT_MISCONFIG]           = handle_ept_misconfig,
 	[EXIT_REASON_PAUSE_INSTRUCTION]       = handle_pause,
@@ -7972,6 +8000,8 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
 		return nested_cpu_has(vmcs12, CPU_BASED_MOV_DR_EXITING);
 	case EXIT_REASON_IO_INSTRUCTION:
 		return nested_vmx_exit_handled_io(vcpu, vmcs12);
+	case EXIT_REASON_GDTR_IDTR: case EXIT_REASON_LDTR_TR:
+		return nested_cpu_has2(vmcs12, SECONDARY_EXEC_DESC);
 	case EXIT_REASON_MSR_READ:
 	case EXIT_REASON_MSR_WRITE:
 		return nested_vmx_exit_handled_msr(vcpu, vmcs12, exit_reason);
@@ -8597,7 +8627,8 @@ static bool vmx_xsaves_supported(void)
 
 static bool vmx_umip_emulated(void)
 {
-	return false;
+	return vmcs_config.cpu_based_2nd_exec_ctrl &
+		SECONDARY_EXEC_DESC;
 }
 
 static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
@@ -9173,7 +9204,8 @@ static void vmcs_set_secondary_exec_control(u32 new_ctl)
 	u32 mask =
 		SECONDARY_EXEC_SHADOW_VMCS |
 		SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
-		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
+		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
+		SECONDARY_EXEC_DESC;
 
 	u32 cur_ctl = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
 
-- 
1.8.3.1