The shortlog "x86: KVM: VMX: Wrap GUEST_IA32_DEBUGCTL read/write with access functions" doesn't follow Sean's suggestion (https://github.com/kvm-x86/linux/blob/next/Documentation/process/maintainer-kvm-x86.rst#shortlog). Please modify. Thanks. On 4/16/2025 8:25 AM, Maxim Levitsky wrote: > Instead of reading and writing GUEST_IA32_DEBUGCTL vmcs field directly, > wrap the logic with get/set functions. > > Also move the checks that the guest's supplied value is valid to the new > 'set' function. > > In particular, the above change fixes a minor security issue in which L1 > hypervisor could set the GUEST_IA32_DEBUGCTL, and eventually the host's > MSR_IA32_DEBUGCTL to any value by performing a VM entry to L2 with > VM_ENTRY_LOAD_DEBUG_CONTROLS set. > > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> > --- > arch/x86/kvm/vmx/nested.c | 15 +++++++--- > arch/x86/kvm/vmx/pmu_intel.c | 9 +++--- > arch/x86/kvm/vmx/vmx.c | 58 +++++++++++++++++++++++------------- > arch/x86/kvm/vmx/vmx.h | 3 ++ > 4 files changed, 57 insertions(+), 28 deletions(-) > > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c > index e073e3008b16..b7686569ee09 100644 > --- a/arch/x86/kvm/vmx/nested.c > +++ b/arch/x86/kvm/vmx/nested.c > @@ -2641,6 +2641,7 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12, > struct vcpu_vmx *vmx = to_vmx(vcpu); > struct hv_enlightened_vmcs *evmcs = nested_vmx_evmcs(vmx); > bool load_guest_pdptrs_vmcs12 = false; > + u64 new_debugctl; > > if (vmx->nested.dirty_vmcs12 || nested_vmx_is_evmptr12_valid(vmx)) { > prepare_vmcs02_rare(vmx, vmcs12); > @@ -2653,11 +2654,17 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12, > if (vmx->nested.nested_run_pending && > (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) { > kvm_set_dr(vcpu, 7, vmcs12->guest_dr7); > - vmcs_write64(GUEST_IA32_DEBUGCTL, vmcs12->guest_ia32_debugctl); > + new_debugctl = vmcs12->guest_ia32_debugctl; > } else { > kvm_set_dr(vcpu, 7, vcpu->arch.dr7); > - vmcs_write64(GUEST_IA32_DEBUGCTL, vmx->nested.pre_vmenter_debugctl); > + new_debugctl = vmx->nested.pre_vmenter_debugctl; > } > + > + if (CC(!vmx_set_guest_debugctl(vcpu, new_debugctl, false))) { > + *entry_failure_code = ENTRY_FAIL_DEFAULT; > + return -EINVAL; > + } > + > if (kvm_mpx_supported() && (!vmx->nested.nested_run_pending || > !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS))) > vmcs_write64(GUEST_BNDCFGS, vmx->nested.pre_vmenter_bndcfgs); > @@ -3520,7 +3527,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu, > > if (!vmx->nested.nested_run_pending || > !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) > - vmx->nested.pre_vmenter_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL); > + vmx->nested.pre_vmenter_debugctl = vmx_get_guest_debugctl(vcpu); > if (kvm_mpx_supported() && > (!vmx->nested.nested_run_pending || > !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS))) > @@ -4788,7 +4795,7 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu, > __vmx_set_segment(vcpu, &seg, VCPU_SREG_LDTR); > > kvm_set_dr(vcpu, 7, 0x400); > - vmcs_write64(GUEST_IA32_DEBUGCTL, 0); > + vmx_set_guest_debugctl(vcpu, 0, false); > > if (nested_vmx_load_msr(vcpu, vmcs12->vm_exit_msr_load_addr, > vmcs12->vm_exit_msr_load_count)) > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c > index 8a94b52c5731..f6f448adfb80 100644 > --- a/arch/x86/kvm/vmx/pmu_intel.c > +++ b/arch/x86/kvm/vmx/pmu_intel.c > @@ -19,6 +19,7 @@ > #include "lapic.h" > #include "nested.h" > #include "pmu.h" > +#include "vmx.h" > #include "tdx.h" > > /* > @@ -652,11 +653,11 @@ static void intel_pmu_reset(struct kvm_vcpu *vcpu) > */ > static void intel_pmu_legacy_freezing_lbrs_on_pmi(struct kvm_vcpu *vcpu) > { > - u64 data = vmcs_read64(GUEST_IA32_DEBUGCTL); > + u64 data = vmx_get_guest_debugctl(vcpu); > > if (data & DEBUGCTLMSR_FREEZE_LBRS_ON_PMI) { > data &= ~DEBUGCTLMSR_LBR; > - vmcs_write64(GUEST_IA32_DEBUGCTL, data); > + vmx_set_guest_debugctl(vcpu, data, true); Two questions. 1. why to call vmx_set_guest_debugctl() to do the extra check? currently IA32_DEBUGCTL MSR is always intercepted and it's already checked at vmx_set_msr() and seems unnecessary to check here again. 2. why the argument "host_initiated" is true? It looks the data is not from host. > } > } > > @@ -729,7 +730,7 @@ void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu) > > if (!lbr_desc->event) { > vmx_disable_lbr_msrs_passthrough(vcpu); > - if (vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR) > + if (vmx_get_guest_debugctl(vcpu) & DEBUGCTLMSR_LBR) > goto warn; > if (test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use)) > goto warn; > @@ -751,7 +752,7 @@ void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu) > > static void intel_pmu_cleanup(struct kvm_vcpu *vcpu) > { > - if (!(vmcs_read64(GUEST_IA32_DEBUGCTL) & DEBUGCTLMSR_LBR)) > + if (!(vmx_get_guest_debugctl(vcpu) & DEBUGCTLMSR_LBR)) > intel_pmu_release_guest_lbr_event(vcpu); > } > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index ef2d7208dd20..4237422dc4ed 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -2154,7 +2154,7 @@ int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > msr_info->data = vmx->pt_desc.guest.addr_a[index / 2]; > break; > case MSR_IA32_DEBUGCTLMSR: > - msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL); > + msr_info->data = vmx_get_guest_debugctl(vcpu); > break; > default: > find_uret_msr: > @@ -2194,6 +2194,41 @@ static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated > return debugctl; > } > > +u64 vmx_get_guest_debugctl(struct kvm_vcpu *vcpu) > +{ > + return vmcs_read64(GUEST_IA32_DEBUGCTL); > +} > + > +static void __vmx_set_guest_debugctl(struct kvm_vcpu *vcpu, u64 data) > +{ > + vmcs_write64(GUEST_IA32_DEBUGCTL, data); > +} IMO, it seems unnecessary to add these 2 wrappers since the original code is already intuitive enough and simple. But if you want, please add "inline" before these 2 wrappers. > + > +bool vmx_set_guest_debugctl(struct kvm_vcpu *vcpu, u64 data, bool host_initiated) Since most of code in this function checks guest debugctl, better to rename it to "vmx_check_and_set_guest_debugctl". > +{ > + u64 invalid = data & ~vmx_get_supported_debugctl(vcpu, host_initiated); > + > + if (invalid & (DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR)) { > + kvm_pr_unimpl_wrmsr(vcpu, MSR_IA32_DEBUGCTLMSR, data); > + data &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR); > + invalid &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR); Add space around above 3 "|". > + } > + > + if (invalid) > + return false; > + > + if (is_guest_mode(vcpu) && (get_vmcs12(vcpu)->vm_exit_controls & > + VM_EXIT_SAVE_DEBUG_CONTROLS)) > + get_vmcs12(vcpu)->guest_ia32_debugctl = data; > + > + if (intel_pmu_lbr_is_enabled(vcpu) && !to_vmx(vcpu)->lbr_desc.event && > + (data & DEBUGCTLMSR_LBR)) > + intel_pmu_create_guest_lbr_event(vcpu); > + > + __vmx_set_guest_debugctl(vcpu, data); > + return true; > +} > + > /* > * Writes msr value into the appropriate "register". > * Returns 0 on success, non-0 otherwise. > @@ -2263,26 +2298,9 @@ int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > vmcs_writel(GUEST_SYSENTER_ESP, data); > break; > case MSR_IA32_DEBUGCTLMSR: { > - u64 invalid; > - > - invalid = data & ~vmx_get_supported_debugctl(vcpu, msr_info->host_initiated); > - if (invalid & (DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR)) { > - kvm_pr_unimpl_wrmsr(vcpu, msr_index, data); > - data &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR); > - invalid &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR); > - } > - > - if (invalid) > + if (!vmx_set_guest_debugctl(vcpu, data, msr_info->host_initiated)) > return 1; > > - if (is_guest_mode(vcpu) && get_vmcs12(vcpu)->vm_exit_controls & > - VM_EXIT_SAVE_DEBUG_CONTROLS) > - get_vmcs12(vcpu)->guest_ia32_debugctl = data; > - > - vmcs_write64(GUEST_IA32_DEBUGCTL, data); > - if (intel_pmu_lbr_is_enabled(vcpu) && !to_vmx(vcpu)->lbr_desc.event && > - (data & DEBUGCTLMSR_LBR)) > - intel_pmu_create_guest_lbr_event(vcpu); > return 0; > } > case MSR_IA32_BNDCFGS: > @@ -4795,7 +4813,7 @@ static void init_vmcs(struct vcpu_vmx *vmx) > vmcs_write32(GUEST_SYSENTER_CS, 0); > vmcs_writel(GUEST_SYSENTER_ESP, 0); > vmcs_writel(GUEST_SYSENTER_EIP, 0); > - vmcs_write64(GUEST_IA32_DEBUGCTL, 0); > + __vmx_set_guest_debugctl(&vmx->vcpu, 0); > > if (cpu_has_vmx_tpr_shadow()) { > vmcs_write64(VIRTUAL_APIC_PAGE_ADDR, 0); > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h > index 6d1e40ecc024..8ac46fb47abd 100644 > --- a/arch/x86/kvm/vmx/vmx.h > +++ b/arch/x86/kvm/vmx/vmx.h > @@ -404,6 +404,9 @@ u64 vmx_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu); > > gva_t vmx_get_untagged_addr(struct kvm_vcpu *vcpu, gva_t gva, unsigned int flags); > > +bool vmx_set_guest_debugctl(struct kvm_vcpu *vcpu, u64 value, bool host_initiated); > +u64 vmx_get_guest_debugctl(struct kvm_vcpu *vcpu); > + > static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr, > int type, bool value) > {
