Fred Griffoul <[email protected]> writes: > From: Fred Griffoul <[email protected]> > > Cache enlightened VMCS control fields to prevent TOCTOU races where the > guest could modify hv_clean_fields or hv_enlightenments_control between > multiple accesses during nested VM-entry. > > The cached values ensure consistent behavior across: > - The evmcs-to-vmcs12 copy operations > - MSR bitmap validation > - Clean field checks in prepare_vmcs02_rare() > > This eliminates potential guest-induced inconsistencies in nested > virtualization state management.
Could you please split the commit to simplify the review and bughunting if (when?) issues are discovered? In particular, I would've split this into at least: - hv_flush_hypercall caching/handling - hv_msr_bitmap caching/handling - nested_vmx_is_evmptr12_valid() instead of vmx->nested.hv_evmcs checks - adding 'bool copy' argument to nested_vmx_handle_enlightened_vmptrld() and moving copy_enlightened_to_vmcs12() there from nested_vmx_run() - hv_clean_fields caching/handling. I want to be extra careful with clean fields. I may had forgotten the details since I've implemented it but I still remember some pain over inconsistent state upon migrations, namely commit d6bf71a18c74de61548ddad44ff95306fe85f829 Author: Vitaly Kuznetsov <[email protected]> Date: Wed May 26 15:20:22 2021 +0200 KVM: nVMX: Ignore 'hv_clean_fields' data when eVMCS data is copied in vmx_get_nested_state() Unfortunatelly, I don't think we have good test coverage for all this in 'hyperv_evmcs' selftest :-( I've seen you added evmcs support to 'vmx_l2_switch_test' in this series, thanks a lot for doing that! > > Signed-off-by: Fred Griffoul <[email protected]> > --- > arch/x86/kvm/vmx/hyperv.c | 5 ++-- > arch/x86/kvm/vmx/hyperv.h | 20 +++++++++++++ > arch/x86/kvm/vmx/nested.c | 62 ++++++++++++++++++++++++--------------- > arch/x86/kvm/vmx/vmx.h | 5 +++- > 4 files changed, 65 insertions(+), 27 deletions(-) > > diff --git a/arch/x86/kvm/vmx/hyperv.c b/arch/x86/kvm/vmx/hyperv.c > index fa41d036acd4..961b91b9bd64 100644 > --- a/arch/x86/kvm/vmx/hyperv.c > +++ b/arch/x86/kvm/vmx/hyperv.c > @@ -213,12 +213,11 @@ bool nested_evmcs_l2_tlb_flush_enabled(struct kvm_vcpu > *vcpu) > { > struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu); > struct vcpu_vmx *vmx = to_vmx(vcpu); > - struct hv_enlightened_vmcs *evmcs = vmx->nested.hv_evmcs; > > - if (!hv_vcpu || !evmcs) > + if (!hv_vcpu || !nested_vmx_is_evmptr12_valid(vmx)) > return false; > > - if (!evmcs->hv_enlightenments_control.nested_flush_hypercall) > + if (!vmx->nested.hv_flush_hypercall) > return false; > > return hv_vcpu->vp_assist_page.nested_control.features.directhypercall; > diff --git a/arch/x86/kvm/vmx/hyperv.h b/arch/x86/kvm/vmx/hyperv.h > index 11a339009781..3c7fea501ca5 100644 > --- a/arch/x86/kvm/vmx/hyperv.h > +++ b/arch/x86/kvm/vmx/hyperv.h > @@ -52,6 +52,16 @@ static inline bool guest_cpu_cap_has_evmcs(struct kvm_vcpu > *vcpu) > to_vmx(vcpu)->nested.enlightened_vmcs_enabled; > } > > +static inline u32 nested_evmcs_clean_fields(struct vcpu_vmx *vmx) > +{ > + return vmx->nested.hv_clean_fields; > +} > + > +static inline bool nested_evmcs_msr_bitmap(struct vcpu_vmx *vmx) > +{ > + return vmx->nested.hv_msr_bitmap; > +} > + > u64 nested_get_evmptr(struct kvm_vcpu *vcpu); > uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu); > int nested_enable_evmcs(struct kvm_vcpu *vcpu, > @@ -85,6 +95,16 @@ static inline struct hv_enlightened_vmcs > *nested_vmx_evmcs(struct vcpu_vmx *vmx) > { > return NULL; > } > + > +static inline u32 nested_evmcs_clean_fields(struct vcpu_vmx *vmx) > +{ > + return 0; > +} > + > +static inline bool nested_evmcs_msr_bitmap(struct vcpu_vmx *vmx) > +{ > + return false; > +} > #endif > > #endif /* __KVM_X86_VMX_HYPERV_H */ > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > index cb4b85edcb7a..5790e1a26456 100644 > --- a/arch/x86/kvm/vmx/nested.c > +++ b/arch/x86/kvm/vmx/nested.c > @@ -236,6 +236,9 @@ static inline void nested_release_evmcs(struct kvm_vcpu > *vcpu) > kvm_vcpu_unmap(vcpu, &vmx->nested.hv_evmcs_map); > vmx->nested.hv_evmcs = NULL; > vmx->nested.hv_evmcs_vmptr = EVMPTR_INVALID; > + vmx->nested.hv_clean_fields = 0; > + vmx->nested.hv_msr_bitmap = false; > + vmx->nested.hv_flush_hypercall = false; > > if (hv_vcpu) { > hv_vcpu->nested.pa_page_gpa = INVALID_GPA; > @@ -737,10 +740,10 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct > kvm_vcpu *vcpu, > * and tells KVM (L0) there were no changes in MSR bitmap for L2. > */ > if (!vmx->nested.force_msr_bitmap_recalc) { > - struct hv_enlightened_vmcs *evmcs = nested_vmx_evmcs(vmx); > - > - if (evmcs && evmcs->hv_enlightenments_control.msr_bitmap && > - evmcs->hv_clean_fields & > HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP) > + if (nested_vmx_is_evmptr12_valid(vmx) && > + nested_evmcs_msr_bitmap(vmx) && > + (nested_evmcs_clean_fields(vmx) > + & HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP)) > return true; > } > > @@ -2214,10 +2217,11 @@ static void copy_vmcs12_to_enlightened(struct > vcpu_vmx *vmx) > * instruction. > */ > static enum nested_evmptrld_status nested_vmx_handle_enlightened_vmptrld( > - struct kvm_vcpu *vcpu, bool from_launch) > + struct kvm_vcpu *vcpu, bool from_launch, bool copy) > { > #ifdef CONFIG_KVM_HYPERV > struct vcpu_vmx *vmx = to_vmx(vcpu); > + struct hv_enlightened_vmcs *evmcs; > bool evmcs_gpa_changed = false; > u64 evmcs_gpa; > > @@ -2297,6 +2301,22 @@ static enum nested_evmptrld_status > nested_vmx_handle_enlightened_vmptrld( > vmx->nested.force_msr_bitmap_recalc = true; > } > > + /* Cache evmcs fields to avoid reading evmcs after copy to vmcs12 */ > + evmcs = vmx->nested.hv_evmcs; > + vmx->nested.hv_clean_fields = evmcs->hv_clean_fields; > + vmx->nested.hv_flush_hypercall = > evmcs->hv_enlightenments_control.nested_flush_hypercall; > + vmx->nested.hv_msr_bitmap = evmcs->hv_enlightenments_control.msr_bitmap; > + > + if (copy) { > + struct vmcs12 *vmcs12 = get_vmcs12(vcpu); > + > + if (likely(!vmcs12->hdr.shadow_vmcs)) { > + copy_enlightened_to_vmcs12(vmx, > vmx->nested.hv_clean_fields); > + /* Enlightened VMCS doesn't have launch state */ > + vmcs12->launch_state = !from_launch; > + } > + } > + > return EVMPTRLD_SUCCEEDED; > #else > return EVMPTRLD_DISABLED; > @@ -2655,10 +2675,12 @@ static void vmcs_write_cet_state(struct kvm_vcpu > *vcpu, u64 s_cet, > > static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12) > { > - struct hv_enlightened_vmcs *hv_evmcs = nested_vmx_evmcs(vmx); > + u32 hv_clean_fields = 0; > > - if (!hv_evmcs || !(hv_evmcs->hv_clean_fields & > - HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP2)) { > + if (nested_vmx_is_evmptr12_valid(vmx)) > + hv_clean_fields = nested_evmcs_clean_fields(vmx); > + > + if (!(hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP2)) { > > vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector); > vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector); > @@ -2700,8 +2722,7 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, > struct vmcs12 *vmcs12) > vmx_segment_cache_clear(vmx); > } > > - if (!hv_evmcs || !(hv_evmcs->hv_clean_fields & > - HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1)) { > + if (!(hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1)) { > vmcs_write32(GUEST_SYSENTER_CS, vmcs12->guest_sysenter_cs); > vmcs_writel(GUEST_PENDING_DBG_EXCEPTIONS, > vmcs12->guest_pending_dbg_exceptions); > @@ -2792,7 +2813,7 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct > vmcs12 *vmcs12, > enum vm_entry_failure_code *entry_failure_code) > { > struct vcpu_vmx *vmx = to_vmx(vcpu); > - struct hv_enlightened_vmcs *evmcs = nested_vmx_evmcs(vmx); > + struct hv_enlightened_vmcs *evmcs; > bool load_guest_pdptrs_vmcs12 = false; > > if (vmx->nested.dirty_vmcs12 || nested_vmx_is_evmptr12_valid(vmx)) { > @@ -2800,7 +2821,8 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct > vmcs12 *vmcs12, > vmx->nested.dirty_vmcs12 = false; > > load_guest_pdptrs_vmcs12 = !nested_vmx_is_evmptr12_valid(vmx) || > - !(evmcs->hv_clean_fields & > HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1); > + !(nested_evmcs_clean_fields(vmx) > + & HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP1); > } > > if (vmx->nested.nested_run_pending && > @@ -2929,7 +2951,8 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct > vmcs12 *vmcs12, > * bits when it changes a field in eVMCS. Mark all fields as clean > * here. > */ > - if (nested_vmx_is_evmptr12_valid(vmx)) > + evmcs = nested_vmx_evmcs(vmx); > + if (evmcs) > evmcs->hv_clean_fields |= HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL; > > return 0; > @@ -3477,7 +3500,7 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu) > if (guest_cpu_cap_has_evmcs(vcpu) && > vmx->nested.hv_evmcs_vmptr == EVMPTR_MAP_PENDING) { > enum nested_evmptrld_status evmptrld_status = > - nested_vmx_handle_enlightened_vmptrld(vcpu, false); > + nested_vmx_handle_enlightened_vmptrld(vcpu, false, > false); > > if (evmptrld_status == EVMPTRLD_VMFAIL || > evmptrld_status == EVMPTRLD_ERROR) > @@ -3867,7 +3890,7 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool > launch) > if (!nested_vmx_check_permission(vcpu)) > return 1; > > - evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch); > + evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch, > true); > if (evmptrld_status == EVMPTRLD_ERROR) { > kvm_queue_exception(vcpu, UD_VECTOR); > return 1; > @@ -3893,15 +3916,8 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool > launch) > if (CC(vmcs12->hdr.shadow_vmcs)) > return nested_vmx_failInvalid(vcpu); > > - if (nested_vmx_is_evmptr12_valid(vmx)) { > - struct hv_enlightened_vmcs *evmcs = nested_vmx_evmcs(vmx); > - > - copy_enlightened_to_vmcs12(vmx, evmcs->hv_clean_fields); > - /* Enlightened VMCS doesn't have launch state */ > - vmcs12->launch_state = !launch; > - } else if (enable_shadow_vmcs) { > + if (!nested_vmx_is_evmptr12_valid(vmx) && enable_shadow_vmcs) > copy_shadow_to_vmcs12(vmx); > - } > > /* > * The nested entry process starts with enforcing various prerequisites > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h > index 90fdf130fd85..cda96196c56c 100644 > --- a/arch/x86/kvm/vmx/vmx.h > +++ b/arch/x86/kvm/vmx/vmx.h > @@ -205,8 +205,11 @@ struct nested_vmx { > > #ifdef CONFIG_KVM_HYPERV > gpa_t hv_evmcs_vmptr; > - struct kvm_host_map hv_evmcs_map; > + u32 hv_clean_fields; > + bool hv_msr_bitmap; > + bool hv_flush_hypercall; > struct hv_enlightened_vmcs *hv_evmcs; > + struct kvm_host_map hv_evmcs_map; > #endif > }; -- Vitaly
