From 6cbbaab60ff33f59355492c241318046befd9ffc Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Wed, 12 Jan 2022 18:01:34 +0100 Subject: KVM: nVMX: Allow VMREAD when Enlightened VMCS is in use Hyper-V TLFS explicitly forbids VMREAD and VMWRITE instructions when Enlightened VMCS interface is in use: "Any VMREAD or VMWRITE instructions while an enlightened VMCS is active is unsupported and can result in unexpected behavior."" Windows 11 + WSL2 seems to ignore this, attempts to VMREAD VMCS field 0x4404 ("VM-exit interruption information") are observed. Failing these attempts with nested_vmx_failInvalid() makes such guests unbootable. Microsoft confirms this is a Hyper-V bug and claims that it'll get fixed eventually but for the time being we need a workaround. (Temporary) allow VMREAD to get data from the currently loaded Enlightened VMCS. Note: VMWRITE instructions remain forbidden, it is not clear how to handle them properly and hopefully won't ever be needed. Reviewed-by: Sean Christopherson Signed-off-by: Vitaly Kuznetsov Message-Id: <20220112170134.1904308-6-vkuznets@redhat.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/evmcs.h | 12 +++++++++++ arch/x86/kvm/vmx/nested.c | 55 +++++++++++++++++++++++++++++++++-------------- 2 files changed, 51 insertions(+), 16 deletions(-) diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h index 9bc2521b159e..8d70f9aea94b 100644 --- a/arch/x86/kvm/vmx/evmcs.h +++ b/arch/x86/kvm/vmx/evmcs.h @@ -98,6 +98,18 @@ static __always_inline int evmcs_field_offset(unsigned long field, return evmcs_field->offset; } +static inline u64 evmcs_read_any(struct hv_enlightened_vmcs *evmcs, + unsigned long field, u16 offset) +{ + /* + * vmcs12_read_any() doesn't care whether the supplied structure + * is 'struct vmcs12' or 'struct hv_enlightened_vmcs' as it takes + * the exact offset of the required field, use it for convenience + * here. + */ + return vmcs12_read_any((void *)evmcs, field, offset); +} + #if IS_ENABLED(CONFIG_HYPERV) static __always_inline int get_evmcs_offset(unsigned long field, diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index e614a5555aab..ba34e94049c7 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -7,6 +7,7 @@ #include #include "cpuid.h" +#include "evmcs.h" #include "hyperv.h" #include "mmu.h" #include "nested.h" @@ -5101,27 +5102,49 @@ static int handle_vmread(struct kvm_vcpu *vcpu) if (!nested_vmx_check_permission(vcpu)) return 1; - /* - * In VMX non-root operation, when the VMCS-link pointer is INVALID_GPA, - * any VMREAD sets the ALU flags for VMfailInvalid. - */ - if (vmx->nested.current_vmptr == INVALID_GPA || - (is_guest_mode(vcpu) && - get_vmcs12(vcpu)->vmcs_link_pointer == INVALID_GPA)) - return nested_vmx_failInvalid(vcpu); - /* Decode instruction info and find the field to read */ field = kvm_register_read(vcpu, (((instr_info) >> 28) & 0xf)); - offset = get_vmcs12_field_offset(field); - if (offset < 0) - return nested_vmx_fail(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT); + if (!evmptr_is_valid(vmx->nested.hv_evmcs_vmptr)) { + /* + * In VMX non-root operation, when the VMCS-link pointer is INVALID_GPA, + * any VMREAD sets the ALU flags for VMfailInvalid. + */ + if (vmx->nested.current_vmptr == INVALID_GPA || + (is_guest_mode(vcpu) && + get_vmcs12(vcpu)->vmcs_link_pointer == INVALID_GPA)) + return nested_vmx_failInvalid(vcpu); - if (!is_guest_mode(vcpu) && is_vmcs12_ext_field(field)) - copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12); + offset = get_vmcs12_field_offset(field); + if (offset < 0) + return nested_vmx_fail(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT); + + if (!is_guest_mode(vcpu) && is_vmcs12_ext_field(field)) + copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12); + + /* Read the field, zero-extended to a u64 value */ + value = vmcs12_read_any(vmcs12, field, offset); + } else { + /* + * Hyper-V TLFS (as of 6.0b) explicitly states, that while an + * enlightened VMCS is active VMREAD/VMWRITE instructions are + * unsupported. Unfortunately, certain versions of Windows 11 + * don't comply with this requirement which is not enforced in + * genuine Hyper-V. Allow VMREAD from an enlightened VMCS as a + * workaround, as misbehaving guests will panic on VM-Fail. + * Note, enlightened VMCS is incompatible with shadow VMCS so + * all VMREADs from L2 should go to L1. + */ + if (WARN_ON_ONCE(is_guest_mode(vcpu))) + return nested_vmx_failInvalid(vcpu); - /* Read the field, zero-extended to a u64 value */ - value = vmcs12_read_any(vmcs12, field, offset); + offset = evmcs_field_offset(field, NULL); + if (offset < 0) + return nested_vmx_fail(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT); + + /* Read the field, zero-extended to a u64 value */ + value = evmcs_read_any(vmx->nested.hv_evmcs, field, offset); + } /* * Now copy part of this value to register or memory, as requested. -- cgit v1.2.3