Fred Griffoul griffoul@gmail.com writes:
From: Fred Griffoul fgriffo@amazon.co.uk
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 vkuznets@redhat.com 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 fgriffo@amazon.co.uk
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 };