KVM: nVMX: vmcs12 checks on nested entry

This patch adds a bunch of tests of the validity of the vmcs12 fields,
according to what the VMX spec and our implementation allows. If fields
we cannot (or don't want to) honor are discovered, an entry failure is
emulated.

According to the spec, there are two types of entry failures: If the problem
was in vmcs12's host state or control fields, the VMLAUNCH instruction simply
fails. But a problem is found in the guest state, the behavior is more
similar to that of an exit.
Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/vmx.h

@@ -430,6 +430,14 @@ struct vmx_msr_entry {
 	u64 value;
 } __aligned(16);
 
+/*
+ * Exit Qualifications for entry failure during or after loading guest state
+ */
+#define ENTRY_FAIL_DEFAULT		0
+#define ENTRY_FAIL_PDPTE		2
+#define ENTRY_FAIL_NMI			3
+#define ENTRY_FAIL_VMCS_LINK_PTR	4
+
 /*
  * VM-instruction error numbers
  */

arch/x86/kvm/vmx.c

@@ -865,6 +865,10 @@ static inline bool nested_cpu_has2(struct vmcs12 *vmcs12, u32 bit)
 		(vmcs12->secondary_vm_exec_control & bit);
 }
 
+static void nested_vmx_entry_failure(struct kvm_vcpu *vcpu,
+			struct vmcs12 *vmcs12,
+			u32 reason, unsigned long qualification);
+
 static int __find_msr_index(struct vcpu_vmx *vmx, u32 msr)
 {
 	int i;
@@ -6116,6 +6120,86 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 	skip_emulated_instruction(vcpu);
 	vmcs12 = get_vmcs12(vcpu);
 
+	/*
+	 * The nested entry process starts with enforcing various prerequisites
+	 * on vmcs12 as required by the Intel SDM, and act appropriately when
+	 * they fail: As the SDM explains, some conditions should cause the
+	 * instruction to fail, while others will cause the instruction to seem
+	 * to succeed, but return an EXIT_REASON_INVALID_STATE.
+	 * To speed up the normal (success) code path, we should avoid checking
+	 * for misconfigurations which will anyway be caught by the processor
+	 * when using the merged vmcs02.
+	 */
+	if (vmcs12->launch_state == launch) {
+		nested_vmx_failValid(vcpu,
+			launch ? VMXERR_VMLAUNCH_NONCLEAR_VMCS
+			       : VMXERR_VMRESUME_NONLAUNCHED_VMCS);
+		return 1;
+	}
+
+	if ((vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_MSR_BITMAPS) &&
+			!IS_ALIGNED(vmcs12->msr_bitmap, PAGE_SIZE)) {
+		/*TODO: Also verify bits beyond physical address width are 0*/
+		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
+		return 1;
+	}
+
+	if (nested_cpu_has2(vmcs12, SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES) &&
+			!IS_ALIGNED(vmcs12->apic_access_addr, PAGE_SIZE)) {
+		/*TODO: Also verify bits beyond physical address width are 0*/
+		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
+		return 1;
+	}
+
+	if (vmcs12->vm_entry_msr_load_count > 0 ||
+	    vmcs12->vm_exit_msr_load_count > 0 ||
+	    vmcs12->vm_exit_msr_store_count > 0) {
+		if (printk_ratelimit())
+			printk(KERN_WARNING
+			  "%s: VMCS MSR_{LOAD,STORE} unsupported\n", __func__);
+		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
+		return 1;
+	}
+
+	if (!vmx_control_verify(vmcs12->cpu_based_vm_exec_control,
+	      nested_vmx_procbased_ctls_low, nested_vmx_procbased_ctls_high) ||
+	    !vmx_control_verify(vmcs12->secondary_vm_exec_control,
+	      nested_vmx_secondary_ctls_low, nested_vmx_secondary_ctls_high) ||
+	    !vmx_control_verify(vmcs12->pin_based_vm_exec_control,
+	      nested_vmx_pinbased_ctls_low, nested_vmx_pinbased_ctls_high) ||
+	    !vmx_control_verify(vmcs12->vm_exit_controls,
+	      nested_vmx_exit_ctls_low, nested_vmx_exit_ctls_high) ||
+	    !vmx_control_verify(vmcs12->vm_entry_controls,
+	      nested_vmx_entry_ctls_low, nested_vmx_entry_ctls_high))
+	{
+		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
+		return 1;
+	}
+
+	if (((vmcs12->host_cr0 & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON) ||
+	    ((vmcs12->host_cr4 & VMXON_CR4_ALWAYSON) != VMXON_CR4_ALWAYSON)) {
+		nested_vmx_failValid(vcpu,
+			VMXERR_ENTRY_INVALID_HOST_STATE_FIELD);
+		return 1;
+	}
+
+	if (((vmcs12->guest_cr0 & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON) ||
+	    ((vmcs12->guest_cr4 & VMXON_CR4_ALWAYSON) != VMXON_CR4_ALWAYSON)) {
+		nested_vmx_entry_failure(vcpu, vmcs12,
+			EXIT_REASON_INVALID_STATE, ENTRY_FAIL_DEFAULT);
+		return 1;
+	}
+	if (vmcs12->vmcs_link_pointer != -1ull) {
+		nested_vmx_entry_failure(vcpu, vmcs12,
+			EXIT_REASON_INVALID_STATE, ENTRY_FAIL_VMCS_LINK_PTR);
+		return 1;
+	}
+
+	/*
+	 * We're finally done with prerequisite checking, and can start with
+	 * the nested entry.
+	 */
+
 	vmcs02 = nested_get_current_vmcs02(vmx);
 	if (!vmcs02)
 		return -ENOMEM;
@@ -6406,6 +6490,23 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu)
 		nested_vmx_succeed(vcpu);
 }
 
+/*
+ * L1's failure to enter L2 is a subset of a normal exit, as explained in
+ * 23.7 "VM-entry failures during or after loading guest state" (this also
+ * lists the acceptable exit-reason and exit-qualification parameters).
+ * It should only be called before L2 actually succeeded to run, and when
+ * vmcs01 is current (it doesn't leave_guest_mode() or switch vmcss).
+ */
+static void nested_vmx_entry_failure(struct kvm_vcpu *vcpu,
+			struct vmcs12 *vmcs12,
+			u32 reason, unsigned long qualification)
+{
+	load_vmcs12_host_state(vcpu, vmcs12);
+	vmcs12->vm_exit_reason = reason | VMX_EXIT_REASONS_FAILED_VMENTRY;
+	vmcs12->exit_qualification = qualification;
+	nested_vmx_succeed(vcpu);
+}
+
 static int vmx_check_intercept(struct kvm_vcpu *vcpu,
 			       struct x86_instruction_info *info,
 			       enum x86_intercept_stage stage)