Commit message: kvm: nVMX: Don't allow L2 to access the hardware CR8

If L1 does not specify the "use TPR shadow" VM-execution control in
vmcs12, then L0 must specify the "CR8-load exiting" and "CR8-store
exiting" VM-execution controls in vmcs02. Failure to do so will give
the L2 VM unrestricted read/write access to the hardware CR8.

This fixes CVE-2017-12154.

Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
CVE: CVE-2017-12154
CWE: CWE-284
Vulnerability description: The prepare_vmcs02 function in arch/x86/kvm/vmx.c in the Linux kernel through 4.13.3 does not ensure that the "CR8-load exiting" and "CR8-store exiting" L0 vmcs02 controls exist in cases where L1 omits the "use TPR shadow" vmcs12 control, which allows KVM L2 guest OS users to obtain read and write access to the hardware CR8 register.

Project: linux
File: vmx.c

static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
			  bool from_vmentry, u32 *entry_failure_code)
{
	struct vcpu_vmx *vmx = to_vmx(vcpu);
	u32 exec_control, vmcs12_exec_ctrl;

	vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector);
	vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector);
	vmcs_write16(GUEST_SS_SELECTOR, vmcs12->guest_ss_selector);
	vmcs_write16(GUEST_DS_SELECTOR, vmcs12->guest_ds_selector);
	vmcs_write16(GUEST_FS_SELECTOR, vmcs12->guest_fs_selector);
	vmcs_write16(GUEST_GS_SELECTOR, vmcs12->guest_gs_selector);
	vmcs_write16(GUEST_LDTR_SELECTOR, vmcs12->guest_ldtr_selector);
	vmcs_write16(GUEST_TR_SELECTOR, vmcs12->guest_tr_selector);
	vmcs_write32(GUEST_ES_LIMIT, vmcs12->guest_es_limit);
	vmcs_write32(GUEST_CS_LIMIT, vmcs12->guest_cs_limit);
	vmcs_write32(GUEST_SS_LIMIT, vmcs12->guest_ss_limit);
	vmcs_write32(GUEST_DS_LIMIT, vmcs12->guest_ds_limit);
	vmcs_write32(GUEST_FS_LIMIT, vmcs12->guest_fs_limit);
	vmcs_write32(GUEST_GS_LIMIT, vmcs12->guest_gs_limit);
	vmcs_write32(GUEST_LDTR_LIMIT, vmcs12->guest_ldtr_limit);
	vmcs_write32(GUEST_TR_LIMIT, vmcs12->guest_tr_limit);
	vmcs_write32(GUEST_GDTR_LIMIT, vmcs12->guest_gdtr_limit);
	vmcs_write32(GUEST_IDTR_LIMIT, vmcs12->guest_idtr_limit);
	vmcs_write32(GUEST_ES_AR_BYTES, vmcs12->guest_es_ar_bytes);
	vmcs_write32(GUEST_CS_AR_BYTES, vmcs12->guest_cs_ar_bytes);
	vmcs_write32(GUEST_SS_AR_BYTES, vmcs12->guest_ss_ar_bytes);
	vmcs_write32(GUEST_DS_AR_BYTES, vmcs12->guest_ds_ar_bytes);
	vmcs_write32(GUEST_FS_AR_BYTES, vmcs12->guest_fs_ar_bytes);
	vmcs_write32(GUEST_GS_AR_BYTES, vmcs12->guest_gs_ar_bytes);
	vmcs_write32(GUEST_LDTR_AR_BYTES, vmcs12->guest_ldtr_ar_bytes);
	vmcs_write32(GUEST_TR_AR_BYTES, vmcs12->guest_tr_ar_bytes);
	vmcs_writel(GUEST_ES_BASE, vmcs12->guest_es_base);
	vmcs_writel(GUEST_CS_BASE, vmcs12->guest_cs_base);
	vmcs_writel(GUEST_SS_BASE, vmcs12->guest_ss_base);
	vmcs_writel(GUEST_DS_BASE, vmcs12->guest_ds_base);
	vmcs_writel(GUEST_FS_BASE, vmcs12->guest_fs_base);
	vmcs_writel(GUEST_GS_BASE, vmcs12->guest_gs_base);
	vmcs_writel(GUEST_LDTR_BASE, vmcs12->guest_ldtr_base);
	vmcs_writel(GUEST_TR_BASE, vmcs12->guest_tr_base);
	vmcs_writel(GUEST_GDTR_BASE, vmcs12->guest_gdtr_base);
	vmcs_writel(GUEST_IDTR_BASE, vmcs12->guest_idtr_base);

	if (from_vmentry &&
	    (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) {
		kvm_set_dr(vcpu, 7, vmcs12->guest_dr7);
		vmcs_write64(GUEST_IA32_DEBUGCTL, vmcs12->guest_ia32_debugctl);
	} else {
		kvm_set_dr(vcpu, 7, vcpu->arch.dr7);
		vmcs_write64(GUEST_IA32_DEBUGCTL, vmx->nested.vmcs01_debugctl);
	}
	if (from_vmentry) {
		vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
			     vmcs12->vm_entry_intr_info_field);
		vmcs_write32(VM_ENTRY_EXCEPTION_ERROR_CODE,
			     vmcs12->vm_entry_exception_error_code);
		vmcs_write32(VM_ENTRY_INSTRUCTION_LEN,
			     vmcs12->vm_entry_instruction_len);
		vmcs_write32(GUEST_INTERRUPTIBILITY_INFO,
			     vmcs12->guest_interruptibility_info);
		vmx->loaded_vmcs->nmi_known_unmasked =
			!(vmcs12->guest_interruptibility_info & GUEST_INTR_STATE_NMI);
	} else {
		vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0);
	}
	vmcs_write32(GUEST_SYSENTER_CS, vmcs12->guest_sysenter_cs);
	vmx_set_rflags(vcpu, vmcs12->guest_rflags);
	vmcs_writel(GUEST_PENDING_DBG_EXCEPTIONS,
		vmcs12->guest_pending_dbg_exceptions);
	vmcs_writel(GUEST_SYSENTER_ESP, vmcs12->guest_sysenter_esp);
	vmcs_writel(GUEST_SYSENTER_EIP, vmcs12->guest_sysenter_eip);

	if (nested_cpu_has_xsaves(vmcs12))
		vmcs_write64(XSS_EXIT_BITMAP, vmcs12->xss_exit_bitmap);
	vmcs_write64(VMCS_LINK_POINTER, -1ull);

	exec_control = vmcs12->pin_based_vm_exec_control;

	/* Preemption timer setting is only taken from vmcs01.  */
	exec_control &= ~PIN_BASED_VMX_PREEMPTION_TIMER;
	exec_control |= vmcs_config.pin_based_exec_ctrl;
	if (vmx->hv_deadline_tsc == -1)
		exec_control &= ~PIN_BASED_VMX_PREEMPTION_TIMER;

	/* Posted interrupts setting is only taken from vmcs12.  */
	if (nested_cpu_has_posted_intr(vmcs12)) {
		vmx->nested.posted_intr_nv = vmcs12->posted_intr_nv;
		vmx->nested.pi_pending = false;
		vmcs_write16(POSTED_INTR_NV, POSTED_INTR_NESTED_VECTOR);
	} else {
		exec_control &= ~PIN_BASED_POSTED_INTR;
	}

	vmcs_write32(PIN_BASED_VM_EXEC_CONTROL, exec_control);

	vmx->nested.preemption_timer_expired = false;
	if (nested_cpu_has_preemption_timer(vmcs12))
		vmx_start_preemption_timer(vcpu);

	/*
	 * Whether page-faults are trapped is determined by a combination of
	 * 3 settings: PFEC_MASK, PFEC_MATCH and EXCEPTION_BITMAP.PF.
	 * If enable_ept, L0 doesn't care about page faults and we should
	 * set all of these to L1's desires. However, if !enable_ept, L0 does
	 * care about (at least some) page faults, and because it is not easy
	 * (if at all possible?) to merge L0 and L1's desires, we simply ask
	 * to exit on each and every L2 page fault. This is done by setting
	 * MASK=MATCH=0 and (see below) EB.PF=1.
	 * Note that below we don't need special code to set EB.PF beyond the
	 * "or"ing of the EB of vmcs01 and vmcs12, because when enable_ept,
	 * vmcs01's EB.PF is 0 so the "or" will take vmcs12's value, and when
	 * !enable_ept, EB.PF is 1, so the "or" will always be 1.
	 */
	vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK,
		enable_ept ? vmcs12->page_fault_error_code_mask : 0);
	vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH,
		enable_ept ? vmcs12->page_fault_error_code_match : 0);

	if (cpu_has_secondary_exec_ctrls()) {
		exec_control = vmx->secondary_exec_control;

		/* Take the following fields only from vmcs12 */
		exec_control &= ~(SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
				  SECONDARY_EXEC_ENABLE_INVPCID |
				  SECONDARY_EXEC_RDTSCP |
				  SECONDARY_EXEC_XSAVES |
				  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
				  SECONDARY_EXEC_APIC_REGISTER_VIRT |
				  SECONDARY_EXEC_ENABLE_VMFUNC);
		if (nested_cpu_has(vmcs12,
				   CPU_BASED_ACTIVATE_SECONDARY_CONTROLS)) {
			vmcs12_exec_ctrl = vmcs12->secondary_vm_exec_control &
				~SECONDARY_EXEC_ENABLE_PML;
			exec_control |= vmcs12_exec_ctrl;
		}

		/* All VMFUNCs are currently emulated through L0 vmexits.  */
		if (exec_control & SECONDARY_EXEC_ENABLE_VMFUNC)
			vmcs_write64(VM_FUNCTION_CONTROL, 0);

		if (exec_control & SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY) {
			vmcs_write64(EOI_EXIT_BITMAP0,
				vmcs12->eoi_exit_bitmap0);
			vmcs_write64(EOI_EXIT_BITMAP1,
				vmcs12->eoi_exit_bitmap1);
			vmcs_write64(EOI_EXIT_BITMAP2,
				vmcs12->eoi_exit_bitmap2);
			vmcs_write64(EOI_EXIT_BITMAP3,
				vmcs12->eoi_exit_bitmap3);
			vmcs_write16(GUEST_INTR_STATUS,
				vmcs12->guest_intr_status);
		}

		/*
		 * Write an illegal value to APIC_ACCESS_ADDR. Later,
		 * nested_get_vmcs12_pages will either fix it up or
		 * remove the VM execution control.
		 */
		if (exec_control & SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)
			vmcs_write64(APIC_ACCESS_ADDR, -1ull);

		vmcs_write32(SECONDARY_VM_EXEC_CONTROL, exec_control);
	}


	/*
	 * Set host-state according to L0's settings (vmcs12 is irrelevant here)
	 * Some constant fields are set here by vmx_set_constant_host_state().
	 * Other fields are different per CPU, and will be set later when
	 * vmx_vcpu_load() is called, and when vmx_save_host_state() is called.
	 */
	vmx_set_constant_host_state(vmx);

	/*
	 * Set the MSR load/store lists to match L0's settings.
	 */
	vmcs_write32(VM_EXIT_MSR_STORE_COUNT, 0);
	vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, vmx->msr_autoload.nr);
	vmcs_write64(VM_EXIT_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.host));
	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.nr);
	vmcs_write64(VM_ENTRY_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.guest));

	/*
	 * HOST_RSP is normally set correctly in vmx_vcpu_run() just before
	 * entry, but only if the current (host) sp changed from the value
	 * we wrote last (vmx->host_rsp). This cache is no longer relevant
	 * if we switch vmcs, and rather than hold a separate cache per vmcs,
	 * here we just force the write to happen on entry.
	 */
	vmx->host_rsp = 0;

	exec_control = vmx_exec_control(vmx); /* L0's desires */
	exec_control &= ~CPU_BASED_VIRTUAL_INTR_PENDING;
	exec_control &= ~CPU_BASED_VIRTUAL_NMI_PENDING;
	exec_control &= ~CPU_BASED_TPR_SHADOW;
	exec_control |= vmcs12->cpu_based_vm_exec_control;

	/*
	 * Write an illegal value to VIRTUAL_APIC_PAGE_ADDR. Later, if
	 * nested_get_vmcs12_pages can't fix it up, the illegal value
	 * will result in a VM entry failure.
	 */
 	if (exec_control & CPU_BASED_TPR_SHADOW) {
 		vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, -1ull);
 		vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);
 	}
 
 	/*
	 * Merging of IO bitmap not currently supported.
	 * Rather, exit every time.
	 */
	exec_control &= ~CPU_BASED_USE_IO_BITMAPS;
	exec_control |= CPU_BASED_UNCOND_IO_EXITING;

	vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, exec_control);

	/* EXCEPTION_BITMAP and CR0_GUEST_HOST_MASK should basically be the
	 * bitwise-or of what L1 wants to trap for L2, and what we want to
	 * trap. Note that CR0.TS also needs updating - we do this later.
	 */
	update_exception_bitmap(vcpu);
	vcpu->arch.cr0_guest_owned_bits &= ~vmcs12->cr0_guest_host_mask;
	vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);

	/* L2->L1 exit controls are emulated - the hardware exit is to L0 so
	 * we should use its exit controls. Note that VM_EXIT_LOAD_IA32_EFER
	 * bits are further modified by vmx_set_efer() below.
	 */
	vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl);

	/* vmcs12's VM_ENTRY_LOAD_IA32_EFER and VM_ENTRY_IA32E_MODE are
	 * emulated by vmx_set_efer(), below.
	 */
	vm_entry_controls_init(vmx, 
		(vmcs12->vm_entry_controls & ~VM_ENTRY_LOAD_IA32_EFER &
			~VM_ENTRY_IA32E_MODE) |
		(vmcs_config.vmentry_ctrl & ~VM_ENTRY_IA32E_MODE));

	if (from_vmentry &&
	    (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PAT)) {
		vmcs_write64(GUEST_IA32_PAT, vmcs12->guest_ia32_pat);
		vcpu->arch.pat = vmcs12->guest_ia32_pat;
	} else if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
		vmcs_write64(GUEST_IA32_PAT, vmx->vcpu.arch.pat);
	}

	set_cr4_guest_host_mask(vmx);

	if (from_vmentry &&
	    vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)
		vmcs_write64(GUEST_BNDCFGS, vmcs12->guest_bndcfgs);

	if (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING)
		vmcs_write64(TSC_OFFSET,
			vcpu->arch.tsc_offset + vmcs12->tsc_offset);
	else
		vmcs_write64(TSC_OFFSET, vcpu->arch.tsc_offset);
	if (kvm_has_tsc_control)
		decache_tsc_multiplier(vmx);

	if (enable_vpid) {
		/*
		 * There is no direct mapping between vpid02 and vpid12, the
		 * vpid02 is per-vCPU for L0 and reused while the value of
		 * vpid12 is changed w/ one invvpid during nested vmentry.
		 * The vpid12 is allocated by L1 for L2, so it will not
		 * influence global bitmap(for vpid01 and vpid02 allocation)
		 * even if spawn a lot of nested vCPUs.
		 */
		if (nested_cpu_has_vpid(vmcs12) && vmx->nested.vpid02) {
			vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->nested.vpid02);
			if (vmcs12->virtual_processor_id != vmx->nested.last_vpid) {
				vmx->nested.last_vpid = vmcs12->virtual_processor_id;
				__vmx_flush_tlb(vcpu, to_vmx(vcpu)->nested.vpid02);
			}
		} else {
			vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
			vmx_flush_tlb(vcpu);
		}

	}

	if (enable_pml) {
		/*
		 * Conceptually we want to copy the PML address and index from
		 * vmcs01 here, and then back to vmcs01 on nested vmexit. But,
		 * since we always flush the log on each vmexit, this happens
		 * to be equivalent to simply resetting the fields in vmcs02.
		 */
		ASSERT(vmx->pml_pg);
		vmcs_write64(PML_ADDRESS, page_to_phys(vmx->pml_pg));
		vmcs_write16(GUEST_PML_INDEX, PML_ENTITY_NUM - 1);
	}

	if (nested_cpu_has_ept(vmcs12)) {
		if (nested_ept_init_mmu_context(vcpu)) {
			*entry_failure_code = ENTRY_FAIL_DEFAULT;
			return 1;
		}
	} else if (nested_cpu_has2(vmcs12,
				   SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
		vmx_flush_tlb_ept_only(vcpu);
	}

	/*
	 * This sets GUEST_CR0 to vmcs12->guest_cr0, possibly modifying those
	 * bits which we consider mandatory enabled.
	 * The CR0_READ_SHADOW is what L2 should have expected to read given
	 * the specifications by L1; It's not enough to take
	 * vmcs12->cr0_read_shadow because on our cr0_guest_host_mask we we
	 * have more bits than L1 expected.
	 */
	vmx_set_cr0(vcpu, vmcs12->guest_cr0);
	vmcs_writel(CR0_READ_SHADOW, nested_read_cr0(vmcs12));

	vmx_set_cr4(vcpu, vmcs12->guest_cr4);
	vmcs_writel(CR4_READ_SHADOW, nested_read_cr4(vmcs12));

	if (from_vmentry &&
	    (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_EFER))
		vcpu->arch.efer = vmcs12->guest_ia32_efer;
	else if (vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE)
		vcpu->arch.efer |= (EFER_LMA | EFER_LME);
	else
		vcpu->arch.efer &= ~(EFER_LMA | EFER_LME);
	/* Note: modifies VM_ENTRY/EXIT_CONTROLS and GUEST/HOST_IA32_EFER */
	vmx_set_efer(vcpu, vcpu->arch.efer);

	/* Shadow page tables on either EPT or shadow page tables. */
	if (nested_vmx_load_cr3(vcpu, vmcs12->guest_cr3, nested_cpu_has_ept(vmcs12),
				entry_failure_code))
		return 1;

	if (!enable_ept)
		vcpu->arch.walk_mmu->inject_page_fault = vmx_inject_page_fault_nested;

	/*
	 * L1 may access the L2's PDPTR, so save them to construct vmcs12
	 */
	if (enable_ept) {
		vmcs_write64(GUEST_PDPTR0, vmcs12->guest_pdptr0);
		vmcs_write64(GUEST_PDPTR1, vmcs12->guest_pdptr1);
		vmcs_write64(GUEST_PDPTR2, vmcs12->guest_pdptr2);
		vmcs_write64(GUEST_PDPTR3, vmcs12->guest_pdptr3);
	}

	kvm_register_write(vcpu, VCPU_REGS_RSP, vmcs12->guest_rsp);
	kvm_register_write(vcpu, VCPU_REGS_RIP, vmcs12->guest_rip);
	return 0;
}