Disallow access (VMREAD/VMWRITE) to fields that the loaded incarnation of KVM doesn't support, e.g. due to lack of hardware support, as a middle ground between allowing access to any vmcs12 field defined by KVM (current behavior) and gating access based on the userspace-defined vCPU model (the most correct, but costly, implementation). Disallowing access to unsupported fields helps a tiny bit in terms of closing the virtualization hole (see below), but the main motivation is to avoid having to weed out unsupported fields when synchronizing between vmcs12 and a shadow VMCS. Because shadow VMCS accesses are done via VMREAD and VMWRITE, KVM _must_ filter out unsupported fields (or eat VMREAD/VMWRITE failures), and filtering out just shadow VMCS fields is about the same amount of effort, and arguably much more confusing. As a bonus, this also fixes a KVM-Unit-Test failure bug when running on _hardware_ without support for TSC Scaling, which fails with the same signature as the bug fixed by commit ba1f82456ba8 ("KVM: nVMX: Dynamically compute max VMCS index for vmcs12"): FAIL: VMX_VMCS_ENUM.MAX_INDEX expected: 19, actual: 17 Dynamically computing the max VMCS index only resolved the issue where KVM was hardcoding max index, but for CPUs with TSC Scaling, that was "good enough". Cc: Yosry Ahmed Link: https://lore.kernel.org/all/20251026201911.505204-22-xin@zytor.com Link: https://lore.kernel.org/all/YR2Tf9WPNEzrE7Xg@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/nested.c | 6 ----- arch/x86/kvm/vmx/vmcs.h | 8 ++++++ arch/x86/kvm/vmx/vmcs12.c | 55 +++++++++++++++++++++++++++++++++++++-- arch/x86/kvm/vmx/vmcs12.h | 8 ++++-- arch/x86/kvm/vmx/vmx.c | 2 ++ 5 files changed, 69 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 6137e5307d0f..9d8f84e3f2da 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -7074,12 +7074,6 @@ void nested_vmx_set_vmcs_shadowing_bitmap(void) } } -/* - * Indexing into the vmcs12 uses the VMCS encoding rotated left by 6. Undo - * that madness to get the encoding for comparison. - */ -#define VMCS12_IDX_TO_ENC(idx) ((u16)(((u16)(idx) >> 6) | ((u16)(idx) << 10))) - static u64 nested_vmx_calc_vmcs_enum_msr(void) { /* diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h index b25625314658..98281e019e38 100644 --- a/arch/x86/kvm/vmx/vmcs.h +++ b/arch/x86/kvm/vmx/vmcs.h @@ -11,7 +11,15 @@ #include "capabilities.h" +/* + * Indexing into the vmcs12 uses the VMCS encoding rotated left by 6 as a very + * rudimentary compression of the range of indices. The compression ratio is + * good enough to allow KVM to use a (very sparsely populated) array without + * wasting too much memory, while the "algorithm" is fast enough to be used to + * lookup vmcs12 fields on-demand, e.g. for emulation. + */ #define ROL16(val, n) ((u16)(((u16)(val) << (n)) | ((u16)(val) >> (16 - (n))))) +#define VMCS12_IDX_TO_ENC(idx) ((u16)(((u16)(idx) >> 6) | ((u16)(idx) << 10))) struct vmcs_hdr { u32 revision_id:31; diff --git a/arch/x86/kvm/vmx/vmcs12.c b/arch/x86/kvm/vmx/vmcs12.c index 4233b5ca9461..78eca9399975 100644 --- a/arch/x86/kvm/vmx/vmcs12.c +++ b/arch/x86/kvm/vmx/vmcs12.c @@ -9,7 +9,7 @@ FIELD(number, name), \ [ROL16(number##_HIGH, 6)] = VMCS12_OFFSET(name) + sizeof(u32) -const unsigned short vmcs12_field_offsets[] = { +const __initconst u16 supported_vmcs12_field_offsets[] = { FIELD(VIRTUAL_PROCESSOR_ID, virtual_processor_id), FIELD(POSTED_INTR_NV, posted_intr_nv), FIELD(GUEST_ES_SELECTOR, guest_es_selector), @@ -158,4 +158,55 @@ const unsigned short vmcs12_field_offsets[] = { FIELD(HOST_SSP, host_ssp), FIELD(HOST_INTR_SSP_TABLE, host_ssp_tbl), }; -const unsigned int nr_vmcs12_fields = ARRAY_SIZE(vmcs12_field_offsets); + +u16 vmcs12_field_offsets[ARRAY_SIZE(supported_vmcs12_field_offsets)] __ro_after_init; +unsigned int nr_vmcs12_fields __ro_after_init; + +#define VMCS12_CASE64(enc) case enc##_HIGH: case enc + +static __init bool cpu_has_vmcs12_field(unsigned int idx) +{ + switch (VMCS12_IDX_TO_ENC(idx)) { + case VIRTUAL_PROCESSOR_ID: return cpu_has_vmx_vpid(); + case POSTED_INTR_NV: return cpu_has_vmx_posted_intr(); + VMCS12_CASE64(TSC_MULTIPLIER): return cpu_has_vmx_tsc_scaling(); + VMCS12_CASE64(VIRTUAL_APIC_PAGE_ADDR): return cpu_has_vmx_tpr_shadow(); + VMCS12_CASE64(APIC_ACCESS_ADDR): return cpu_has_vmx_virtualize_apic_accesses(); + VMCS12_CASE64(POSTED_INTR_DESC_ADDR): return cpu_has_vmx_posted_intr(); + VMCS12_CASE64(VM_FUNCTION_CONTROL): return cpu_has_vmx_vmfunc(); + VMCS12_CASE64(EPT_POINTER): return cpu_has_vmx_ept(); + VMCS12_CASE64(EPTP_LIST_ADDRESS): return cpu_has_vmx_vmfunc(); + VMCS12_CASE64(XSS_EXIT_BITMAP): return cpu_has_vmx_xsaves(); + VMCS12_CASE64(ENCLS_EXITING_BITMAP): return cpu_has_vmx_encls_vmexit(); + VMCS12_CASE64(GUEST_IA32_PERF_GLOBAL_CTRL): return cpu_has_load_perf_global_ctrl(); + VMCS12_CASE64(HOST_IA32_PERF_GLOBAL_CTRL): return cpu_has_load_perf_global_ctrl(); + case TPR_THRESHOLD: return cpu_has_vmx_tpr_shadow(); + case SECONDARY_VM_EXEC_CONTROL: return cpu_has_secondary_exec_ctrls(); + case GUEST_S_CET: return cpu_has_load_cet_ctrl(); + case GUEST_SSP: return cpu_has_load_cet_ctrl(); + case GUEST_INTR_SSP_TABLE: return cpu_has_load_cet_ctrl(); + case HOST_S_CET: return cpu_has_load_cet_ctrl(); + case HOST_SSP: return cpu_has_load_cet_ctrl(); + case HOST_INTR_SSP_TABLE: return cpu_has_load_cet_ctrl(); + + /* KVM always emulates PML and the VMX preemption timer in software. */ + case GUEST_PML_INDEX: + case VMX_PREEMPTION_TIMER_VALUE: + default: + return true; + } +} + +void __init nested_vmx_setup_vmcs12_fields(void) +{ + unsigned int i; + + for (i = 0; i < ARRAY_SIZE(supported_vmcs12_field_offsets); i++) { + if (!supported_vmcs12_field_offsets[i] || + !cpu_has_vmcs12_field(i)) + continue; + + vmcs12_field_offsets[i] = supported_vmcs12_field_offsets[i]; + nr_vmcs12_fields = i + 1; + } +} diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h index 4ad6b16525b9..e5905ba0bb42 100644 --- a/arch/x86/kvm/vmx/vmcs12.h +++ b/arch/x86/kvm/vmx/vmcs12.h @@ -374,8 +374,12 @@ static inline void vmx_check_vmcs12_offsets(void) CHECK_OFFSET(guest_pml_index, 996); } -extern const unsigned short vmcs12_field_offsets[]; -extern const unsigned int nr_vmcs12_fields; +extern const __initconst u16 supported_vmcs12_field_offsets[]; + +extern u16 vmcs12_field_offsets[] __ro_after_init; +extern unsigned int nr_vmcs12_fields __ro_after_init; + +void __init nested_vmx_setup_vmcs12_fields(void); static inline short get_vmcs12_field_offset(unsigned long field) { diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 6b96f7aea20b..e5ad3853f51d 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -8670,6 +8670,8 @@ __init int vmx_hardware_setup(void) * can hide/show features based on kvm_cpu_cap_has(). */ if (nested) { + nested_vmx_setup_vmcs12_fields(); + nested_vmx_setup_ctls_msrs(&vmcs_config, vmx_capability.ept); r = nested_vmx_hardware_setup(kvm_vmx_exit_handlers); base-commit: 58e10b63777d0aebee2cf4e6c67e1a83e7edbe0f -- 2.52.0.239.gd5f0c6e74e-goog