From: Oliver Upton Date: Tue, 18 Aug 2020 15:24:28 +0000 (+0000) Subject: kvm: x86: only provide PV features if enabled in guest's CPUID X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=66570e966dd9cb4f;p=linux.git kvm: x86: only provide PV features if enabled in guest's CPUID KVM unconditionally provides PV features to the guest, regardless of the configured CPUID. An unwitting guest that doesn't check KVM_CPUID_FEATURES before use could access paravirt features that userspace did not intend to provide. Fix this by checking the guest's CPUID before performing any paravirtual operations. Introduce a capability, KVM_CAP_ENFORCE_PV_FEATURE_CPUID, to gate the aforementioned enforcement. Migrating a VM from a host w/o this patch to a host with this patch could silently change the ABI exposed to the guest, warranting that we default to the old behavior and opt-in for the new one. Reviewed-by: Jim Mattson Reviewed-by: Peter Shier Signed-off-by: Oliver Upton Change-Id: I202a0926f65035b872bfe8ad15307c026de59a98 Message-Id: <20200818152429.1923996-4-oupton@google.com> Reviewed-by: Wanpeng Li Signed-off-by: Paolo Bonzini --- diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 9ece9a827a581..76317221d29fb 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6380,3 +6380,14 @@ ranges that KVM should reject access to. In combination with KVM_CAP_X86_USER_SPACE_MSR, this allows user space to trap and emulate MSRs that are outside of the scope of KVM as well as limit the attack surface on KVM's MSR emulation code. + + +8.26 KVM_CAP_ENFORCE_PV_CPUID +----------------------------- + +Architectures: x86 + +When enabled, KVM will disable paravirtual features provided to the +guest according to the bits in the KVM_CPUID_FEATURES CPUID leaf +(0x40000001). Otherwise, a guest may use the paravirtual features +regardless of what has actually been exposed through the CPUID leaf. diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index d0f77235da923..15e51343957e2 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -789,6 +789,21 @@ struct kvm_vcpu_arch { /* AMD MSRC001_0015 Hardware Configuration */ u64 msr_hwcr; + + /* pv related cpuid info */ + struct { + /* + * value of the eax register in the KVM_CPUID_FEATURES CPUID + * leaf. + */ + u32 features; + + /* + * indicates whether pv emulation should be disabled if features + * are not present in the guest's cpuid + */ + bool enforce; + } pv_cpuid; }; struct kvm_lpage_info { diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 37c3668a774f5..d253c023ee766 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -107,6 +107,13 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu) (best->eax & (1 << KVM_FEATURE_PV_UNHALT))) best->eax &= ~(1 << KVM_FEATURE_PV_UNHALT); + /* + * save the feature bitmap to avoid cpuid lookup for every PV + * operation + */ + if (best) + vcpu->arch.pv_cpuid.features = best->eax; + if (!kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT)) { best = kvm_find_cpuid_entry(vcpu, 0x1, 0); if (best) diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h index 1d2c4f2e4bb6f..bf8577947ed23 100644 --- a/arch/x86/kvm/cpuid.h +++ b/arch/x86/kvm/cpuid.h @@ -5,6 +5,7 @@ #include "x86.h" #include #include +#include extern u32 kvm_cpu_caps[NCAPINTS] __read_mostly; void kvm_set_cpu_caps(void); @@ -313,4 +314,13 @@ static inline bool page_address_valid(struct kvm_vcpu *vcpu, gpa_t gpa) return PAGE_ALIGNED(gpa) && !(gpa >> cpuid_maxphyaddr(vcpu)); } +static __always_inline bool guest_pv_has(struct kvm_vcpu *vcpu, + unsigned int kvm_feature) +{ + if (!vcpu->arch.pv_cpuid.enforce) + return true; + + return vcpu->arch.pv_cpuid.features & (1u << kvm_feature); +} + #endif diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b928e092da037..ca940de53e182 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2877,6 +2877,14 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data) if (data & 0x30) return 1; + if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF_VMEXIT) && + (data & KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT)) + return 1; + + if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF_INT) && + (data & KVM_ASYNC_PF_DELIVERY_AS_INT)) + return 1; + if (!lapic_in_kernel(vcpu)) return data ? 1 : 0; @@ -2954,10 +2962,12 @@ static void record_steal_time(struct kvm_vcpu *vcpu) * Doing a TLB flush here, on the guest's behalf, can avoid * expensive IPIs. */ - trace_kvm_pv_tlb_flush(vcpu->vcpu_id, - st->preempted & KVM_VCPU_FLUSH_TLB); - if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB) - kvm_vcpu_flush_tlb_guest(vcpu); + if (guest_pv_has(vcpu, KVM_FEATURE_PV_TLB_FLUSH)) { + trace_kvm_pv_tlb_flush(vcpu->vcpu_id, + st->preempted & KVM_VCPU_FLUSH_TLB); + if (xchg(&st->preempted, 0) & KVM_VCPU_FLUSH_TLB) + kvm_vcpu_flush_tlb_guest(vcpu); + } vcpu->arch.st.preempted = 0; @@ -3118,30 +3128,54 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) vcpu->arch.smi_count = data; break; case MSR_KVM_WALL_CLOCK_NEW: + if (!guest_pv_has(vcpu, KVM_FEATURE_CLOCKSOURCE2)) + return 1; + + kvm_write_wall_clock(vcpu->kvm, data); + break; case MSR_KVM_WALL_CLOCK: + if (!guest_pv_has(vcpu, KVM_FEATURE_CLOCKSOURCE)) + return 1; + kvm_write_wall_clock(vcpu->kvm, data); break; case MSR_KVM_SYSTEM_TIME_NEW: + if (!guest_pv_has(vcpu, KVM_FEATURE_CLOCKSOURCE2)) + return 1; + kvm_write_system_time(vcpu, data, false, msr_info->host_initiated); break; case MSR_KVM_SYSTEM_TIME: - kvm_write_system_time(vcpu, data, true, msr_info->host_initiated); + if (!guest_pv_has(vcpu, KVM_FEATURE_CLOCKSOURCE)) + return 1; + + kvm_write_system_time(vcpu, data, true, msr_info->host_initiated); break; case MSR_KVM_ASYNC_PF_EN: + if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF)) + return 1; + if (kvm_pv_enable_async_pf(vcpu, data)) return 1; break; case MSR_KVM_ASYNC_PF_INT: + if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF_INT)) + return 1; + if (kvm_pv_enable_async_pf_int(vcpu, data)) return 1; break; case MSR_KVM_ASYNC_PF_ACK: + if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF)) + return 1; if (data & 0x1) { vcpu->arch.apf.pageready_pending = false; kvm_check_async_pf_completion(vcpu); } break; case MSR_KVM_STEAL_TIME: + if (!guest_pv_has(vcpu, KVM_FEATURE_STEAL_TIME)) + return 1; if (unlikely(!sched_info_on())) return 1; @@ -3158,11 +3192,17 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) break; case MSR_KVM_PV_EOI_EN: + if (!guest_pv_has(vcpu, KVM_FEATURE_PV_EOI)) + return 1; + if (kvm_lapic_enable_pv_eoi(vcpu, data, sizeof(u8))) return 1; break; case MSR_KVM_POLL_CONTROL: + if (!guest_pv_has(vcpu, KVM_FEATURE_POLL_CONTROL)) + return 1; + /* only enable bit supported */ if (data & (-1ULL << 1)) return 1; @@ -3658,6 +3698,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_LAST_CPU: case KVM_CAP_X86_USER_SPACE_MSR: case KVM_CAP_X86_MSR_FILTER: + case KVM_CAP_ENFORCE_PV_FEATURE_CPUID: r = 1; break; case KVM_CAP_SYNC_REGS: @@ -4528,6 +4569,11 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu, return kvm_x86_ops.enable_direct_tlbflush(vcpu); + case KVM_CAP_ENFORCE_PV_FEATURE_CPUID: + vcpu->arch.pv_cpuid.enforce = cap->args[0]; + + return 0; + default: return -EINVAL; } @@ -8000,11 +8046,16 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) goto out; } + ret = -KVM_ENOSYS; + switch (nr) { case KVM_HC_VAPIC_POLL_IRQ: ret = 0; break; case KVM_HC_KICK_CPU: + if (!guest_pv_has(vcpu, KVM_FEATURE_PV_UNHALT)) + break; + kvm_pv_kick_cpu_op(vcpu->kvm, a0, a1); kvm_sched_yield(vcpu->kvm, a1); ret = 0; @@ -8015,9 +8066,15 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) break; #endif case KVM_HC_SEND_IPI: + if (!guest_pv_has(vcpu, KVM_FEATURE_PV_SEND_IPI)) + break; + ret = kvm_pv_send_ipi(vcpu->kvm, a0, a1, a2, a3, op_64_bit); break; case KVM_HC_SCHED_YIELD: + if (!guest_pv_has(vcpu, KVM_FEATURE_PV_SCHED_YIELD)) + break; + kvm_sched_yield(vcpu->kvm, a0); ret = 0; break; diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 58f43aa1fc211..ca41220b40b8b 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1052,6 +1052,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_STEAL_TIME 187 #define KVM_CAP_X86_USER_SPACE_MSR 188 #define KVM_CAP_X86_MSR_FILTER 189 +#define KVM_CAP_ENFORCE_PV_FEATURE_CPUID 190 #ifdef KVM_CAP_IRQ_ROUTING