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[52.49.196.232]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47be27b0d5asm806409235e9.13.2026.01.02.06.24.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Jan 2026 06:24:42 -0800 (PST) From: Fred Griffoul To: kvm@vger.kernel.org Cc: seanjc@google.com, pbonzini@redhat.com, vkuznets@redhat.com, shuah@kernel.org, dwmw@amazon.co.uk, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Fred Griffoul Subject: [PATCH v4 06/10] KVM: nVMX: Cache evmcs fields to ensure consistency during VM-entry Date: Fri, 2 Jan 2026 14:24:25 +0000 Message-ID: <20260102142429.896101-7-griffoul@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260102142429.896101-1-griffoul@gmail.com> References: <20260102142429.896101-1-griffoul@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Fred Griffoul 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. Signed-off-by: Fred Griffoul --- 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_vcp= u *vcpu) { struct kvm_vcpu_hv *hv_vcpu =3D to_hv_vcpu(vcpu); struct vcpu_vmx *vmx =3D to_vmx(vcpu); - struct hv_enlightened_vmcs *evmcs =3D vmx->nested.hv_evmcs; =20 - if (!hv_vcpu || !evmcs) + if (!hv_vcpu || !nested_vmx_is_evmptr12_valid(vmx)) return false; =20 - if (!evmcs->hv_enlightenments_control.nested_flush_hypercall) + if (!vmx->nested.hv_flush_hypercall) return false; =20 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_vc= pu *vcpu) to_vmx(vcpu)->nested.enlightened_vmcs_enabled; } =20 +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_evm= cs(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 =20 #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 =3D NULL; vmx->nested.hv_evmcs_vmptr =3D EVMPTR_INVALID; + vmx->nested.hv_clean_fields =3D 0; + vmx->nested.hv_msr_bitmap =3D false; + vmx->nested.hv_flush_hypercall =3D false; =20 if (hv_vcpu) { hv_vcpu->nested.pa_page_gpa =3D INVALID_GPA; @@ -737,10 +740,10 @@ static inline bool nested_vmx_prepare_msr_bitmap(stru= ct 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 =3D 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; } =20 @@ -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 =3D to_vmx(vcpu); + struct hv_enlightened_vmcs *evmcs; bool evmcs_gpa_changed =3D false; u64 evmcs_gpa; =20 @@ -2297,6 +2301,22 @@ static enum nested_evmptrld_status nested_vmx_handle= _enlightened_vmptrld( vmx->nested.force_msr_bitmap_recalc =3D true; } =20 + /* Cache evmcs fields to avoid reading evmcs after copy to vmcs12 */ + evmcs =3D vmx->nested.hv_evmcs; + vmx->nested.hv_clean_fields =3D evmcs->hv_clean_fields; + vmx->nested.hv_flush_hypercall =3D evmcs->hv_enlightenments_control.neste= d_flush_hypercall; + vmx->nested.hv_msr_bitmap =3D evmcs->hv_enlightenments_control.msr_bitmap; + + if (copy) { + struct vmcs12 *vmcs12 =3D 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 =3D !from_launch; + } + } + return EVMPTRLD_SUCCEEDED; #else return EVMPTRLD_DISABLED; @@ -2655,10 +2675,12 @@ static void vmcs_write_cet_state(struct kvm_vcpu *v= cpu, u64 s_cet, =20 static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs1= 2) { - struct hv_enlightened_vmcs *hv_evmcs =3D nested_vmx_evmcs(vmx); + u32 hv_clean_fields =3D 0; =20 - 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 =3D nested_evmcs_clean_fields(vmx); + + if (!(hv_clean_fields & HV_VMX_ENLIGHTENED_CLEAN_FIELD_GUEST_GRP2)) { =20 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); } =20 - 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, stru= ct vmcs12 *vmcs12, enum vm_entry_failure_code *entry_failure_code) { struct vcpu_vmx *vmx =3D to_vmx(vcpu); - struct hv_enlightened_vmcs *evmcs =3D nested_vmx_evmcs(vmx); + struct hv_enlightened_vmcs *evmcs; bool load_guest_pdptrs_vmcs12 =3D false; =20 if (vmx->nested.dirty_vmcs12 || nested_vmx_is_evmptr12_valid(vmx)) { @@ -2800,7 +2821,8 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, stru= ct vmcs12 *vmcs12, vmx->nested.dirty_vmcs12 =3D false; =20 load_guest_pdptrs_vmcs12 =3D !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); } =20 if (vmx->nested.nested_run_pending && @@ -2929,7 +2951,8 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, stru= ct vmcs12 *vmcs12, * bits when it changes a field in eVMCS. Mark all fields as clean * here. */ - if (nested_vmx_is_evmptr12_valid(vmx)) + evmcs =3D nested_vmx_evmcs(vmx); + if (evmcs) evmcs->hv_clean_fields |=3D HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL; =20 return 0; @@ -3477,7 +3500,7 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vc= pu) if (guest_cpu_cap_has_evmcs(vcpu) && vmx->nested.hv_evmcs_vmptr =3D=3D EVMPTR_MAP_PENDING) { enum nested_evmptrld_status evmptrld_status =3D - nested_vmx_handle_enlightened_vmptrld(vcpu, false); + nested_vmx_handle_enlightened_vmptrld(vcpu, false, false); =20 if (evmptrld_status =3D=3D EVMPTRLD_VMFAIL || evmptrld_status =3D=3D 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; =20 - evmptrld_status =3D nested_vmx_handle_enlightened_vmptrld(vcpu, launch); + evmptrld_status =3D nested_vmx_handle_enlightened_vmptrld(vcpu, launch, t= rue); if (evmptrld_status =3D=3D EVMPTRLD_ERROR) { kvm_queue_exception(vcpu, UD_VECTOR); return 1; @@ -3893,15 +3916,8 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, boo= l launch) if (CC(vmcs12->hdr.shadow_vmcs)) return nested_vmx_failInvalid(vcpu); =20 - if (nested_vmx_is_evmptr12_valid(vmx)) { - struct hv_enlightened_vmcs *evmcs =3D nested_vmx_evmcs(vmx); - - copy_enlightened_to_vmcs12(vmx, evmcs->hv_clean_fields); - /* Enlightened VMCS doesn't have launch state */ - vmcs12->launch_state =3D !launch; - } else if (enable_shadow_vmcs) { + if (!nested_vmx_is_evmptr12_valid(vmx) && enable_shadow_vmcs) copy_shadow_to_vmcs12(vmx); - } =20 /* * 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 { =20 #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 }; =20 --=20 2.43.0