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This event serves a nearly identical purpose to the previously-added SNP_GUEST_REQUEST event, but allows for additional certificate data to be supplied via an additional guest-supplied buffer to be used mainly for verifying the signature of an attestation report as returned by firmware. This certificate data is supplied by userspace, so unlike with SNP_GUEST_REQUEST events, SNP_EXTENDED_GUEST_REQUEST events are first forwarded to userspace via a KVM_EXIT_VMGEXIT exit type, and then the firmware request is made only afterward. Implement handling for these events. Since there is a potential for race conditions where the userspace-supplied certificate data may be out-of-sync relative to the reported TCB or VLEK that firmware will use when signing attestation reports, make use of the synchronization mechanisms wired up to the SNP_{PAUSE,RESUME}_ATTESTATION SEV device ioctls such that the guest will be told to retry the request while attestation has been paused due to an update being underway on the system. Signed-off-by: Michael Roth --- Documentation/virt/kvm/api.rst | 26 +++++++++++ arch/x86/include/asm/sev.h | 6 +++ arch/x86/kvm/svm/sev.c | 82 ++++++++++++++++++++++++++++++++++ arch/x86/kvm/svm/svm.h | 3 ++ arch/x86/virt/svm/sev.c | 37 +++++++++++++++ include/uapi/linux/kvm.h | 6 +++ 6 files changed, 160 insertions(+) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 85099198a10f..6cf186ed8f66 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7066,6 +7066,7 @@ values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set. struct kvm_user_vmgexit { #define KVM_USER_VMGEXIT_PSC_MSR 1 #define KVM_USER_VMGEXIT_PSC 2 + #define KVM_USER_VMGEXIT_EXT_GUEST_REQ 3 __u32 type; /* KVM_USER_VMGEXIT_* type */ union { struct { @@ -7079,6 +7080,11 @@ values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set. __u64 shared_gpa; __u64 ret; } psc; + struct { + __u64 data_gpa; + __u64 data_npages; + __u32 ret; + } ext_guest_req; }; }; @@ -7108,6 +7114,26 @@ private/shared state. Userspace will return a value in 'ret' that is in agreement with the GHCB-defined return values that the guest will expect in the SW_EXITINFO2 field of the GHCB in response to these requests. +For the KVM_USER_VMGEXIT_EXT_GUEST_REQ type, the ext_guest_req union type +is used. The kernel will supply in 'data_gpa' the value the guest supplies +via the RAX field of the GHCB when issued extended guest requests. +'data_npages' will similarly contain the value the guest supplies in RBX +denoting the number of shared pages available to write the certificate +data into. + + - If the supplied number of pages is sufficient, userspace should write + the certificate data blob (in the format defined by the GHCB spec) in + the address indicated by 'data_gpa' and set 'ret' to 0. + + - If the number of pages supplied is not sufficient, userspace must write + the required number of pages in 'data_npages' and then set 'ret' to 1. + + - If userspace is temporarily unable to handle the request, 'ret' should + be set to 2 to inform the guest to retry later. + + - If some other error occurred, userspace should set 'ret' to a non-zero + value that is distinct from the specific return values mentioned above. + 6. Capabilities that can be enabled on vCPUs ============================================ diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h index ee24ef815e35..dfc28ac4dd0e 100644 --- a/arch/x86/include/asm/sev.h +++ b/arch/x86/include/asm/sev.h @@ -276,6 +276,9 @@ void snp_leak_pages(u64 pfn, unsigned int npages); void kdump_sev_callback(void); int snp_pause_attestation(u64 *transaction_id); void snp_resume_attestation(u64 *transaction_id); +u64 snp_transaction_get_id(void); +bool __snp_transaction_is_stale(u64 transaction_id); +bool snp_transaction_is_stale(u64 transaction_id); #else static inline bool snp_probe_rmptable_info(void) { return false; } static inline int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level) { return -ENODEV; } @@ -291,6 +294,9 @@ static inline void snp_leak_pages(u64 pfn, unsigned int npages) {} static inline void kdump_sev_callback(void) { } static inline int snp_pause_attestation(u64 *transaction_id) { return 0; } static inline void snp_resume_attestation(u64 *transaction_id) {} +static inline u64 snp_transaction_get_id(void) { return 0; } +static inline bool __snp_transaction_is_stale(u64 transaction_id) { return false; } +static inline bool snp_transaction_is_stale(u64 transaction_id) { return false; } #endif #endif diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 68db390b19d0..1cec466e593b 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -3292,6 +3292,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm) case SVM_VMGEXIT_PSC: case SVM_VMGEXIT_TERM_REQUEST: case SVM_VMGEXIT_GUEST_REQUEST: + case SVM_VMGEXIT_EXT_GUEST_REQUEST: break; default: reason = GHCB_ERR_INVALID_EVENT; @@ -3812,6 +3813,84 @@ static void snp_handle_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err)); } +static int snp_complete_ext_guest_req(struct kvm_vcpu *vcpu) +{ + struct vcpu_svm *svm = to_svm(vcpu); + struct vmcb_control_area *control; + struct kvm *kvm = vcpu->kvm; + sev_ret_code fw_err = 0; + int vmm_ret; + + vmm_ret = vcpu->run->vmgexit.ext_guest_req.ret; + if (vmm_ret) { + if (vmm_ret == SNP_GUEST_VMM_ERR_INVALID_LEN) + vcpu->arch.regs[VCPU_REGS_RBX] = + vcpu->run->vmgexit.ext_guest_req.data_npages; + goto abort_request; + } + + control = &svm->vmcb->control; + + /* + * To avoid the message sequence number getting out of sync between the + * actual value seen by firmware verses the value expected by the guest, + * make sure attestations can't get paused on the write-side at this + * point by holding the lock for the entire duration of the firmware + * request so that there is no situation where SNP_GUEST_VMM_ERR_BUSY + * would need to be returned after firmware sees the request. + */ + mutex_lock(&snp_pause_attestation_lock); + + if (__snp_transaction_is_stale(svm->snp_transaction_id)) + vmm_ret = SNP_GUEST_VMM_ERR_BUSY; + else if (!__snp_handle_guest_req(kvm, control->exit_info_1, + control->exit_info_2, &fw_err)) + vmm_ret = SNP_GUEST_VMM_ERR_GENERIC; + + mutex_unlock(&snp_pause_attestation_lock); + +abort_request: + ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err)); + + return 1; /* resume guest */ +} + +static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu) +{ + int vmm_ret = SNP_GUEST_VMM_ERR_GENERIC; + struct vcpu_svm *svm = to_svm(vcpu); + unsigned long data_npages; + sev_ret_code fw_err; + gpa_t data_gpa; + + if (!sev_snp_guest(vcpu->kvm)) + goto abort_request; + + data_gpa = vcpu->arch.regs[VCPU_REGS_RAX]; + data_npages = vcpu->arch.regs[VCPU_REGS_RBX]; + + if (!IS_ALIGNED(data_gpa, PAGE_SIZE)) + goto abort_request; + + svm->snp_transaction_id = snp_transaction_get_id(); + if (snp_transaction_is_stale(svm->snp_transaction_id)) { + vmm_ret = SNP_GUEST_VMM_ERR_BUSY; + goto abort_request; + } + + vcpu->run->exit_reason = KVM_EXIT_VMGEXIT; + vcpu->run->vmgexit.type = KVM_USER_VMGEXIT_EXT_GUEST_REQ; + vcpu->run->vmgexit.ext_guest_req.data_gpa = data_gpa; + vcpu->run->vmgexit.ext_guest_req.data_npages = data_npages; + vcpu->arch.complete_userspace_io = snp_complete_ext_guest_req; + + return 0; /* forward request to userspace */ + +abort_request: + ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err)); + return 1; /* resume guest */ +} + static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm) { struct vmcb_control_area *control = &svm->vmcb->control; @@ -4076,6 +4155,9 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu) snp_handle_guest_req(svm, control->exit_info_1, control->exit_info_2); ret = 1; break; + case SVM_VMGEXIT_EXT_GUEST_REQUEST: + ret = snp_begin_ext_guest_req(vcpu); + break; case SVM_VMGEXIT_UNSUPPORTED_EVENT: vcpu_unimpl(vcpu, "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n", diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 8a8ee475ad86..28140bc8af27 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -303,6 +303,9 @@ struct vcpu_svm { /* Guest GIF value, used when vGIF is not enabled */ bool guest_gif; + + /* Transaction ID associated with SNP config updates */ + u64 snp_transaction_id; }; struct svm_cpu_data { diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c index b75f2e7d4012..f1f7486a3dcf 100644 --- a/arch/x86/virt/svm/sev.c +++ b/arch/x86/virt/svm/sev.c @@ -72,6 +72,7 @@ static unsigned long snp_nr_leaked_pages; /* For synchronizing TCB/certificate updates with extended guest requests */ DEFINE_MUTEX(snp_pause_attestation_lock); +EXPORT_SYMBOL_GPL(snp_pause_attestation_lock); static u64 snp_transaction_id; static bool snp_attestation_paused; @@ -611,3 +612,39 @@ void snp_resume_attestation(u64 *transaction_id) mutex_unlock(&snp_pause_attestation_lock); } EXPORT_SYMBOL_GPL(snp_resume_attestation); + +u64 snp_transaction_get_id(void) +{ + u64 id; + + mutex_lock(&snp_pause_attestation_lock); + id = snp_transaction_id; + mutex_unlock(&snp_pause_attestation_lock); + + return id; +} +EXPORT_SYMBOL_GPL(snp_transaction_get_id); + +/* Must be called with snp_pause_attestion_lock held */ +bool __snp_transaction_is_stale(u64 transaction_id) +{ + lockdep_assert_held(&snp_pause_attestation_lock); + + return (snp_attestation_paused || + transaction_id != snp_transaction_id); +} +EXPORT_SYMBOL_GPL(__snp_transaction_is_stale); + +bool snp_transaction_is_stale(u64 transaction_id) +{ + bool stale; + + mutex_lock(&snp_pause_attestation_lock); + + stale = __snp_transaction_is_stale(transaction_id); + + mutex_unlock(&snp_pause_attestation_lock); + + return stale; +} +EXPORT_SYMBOL_GPL(snp_transaction_is_stale); diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index e33c48bfbd67..585de3a2591e 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -138,6 +138,7 @@ struct kvm_xen_exit { struct kvm_user_vmgexit { #define KVM_USER_VMGEXIT_PSC_MSR 1 #define KVM_USER_VMGEXIT_PSC 2 +#define KVM_USER_VMGEXIT_EXT_GUEST_REQ 3 __u32 type; /* KVM_USER_VMGEXIT_* type */ union { struct { @@ -151,6 +152,11 @@ struct kvm_user_vmgexit { __u64 shared_gpa; __u64 ret; } psc; + struct { + __u64 data_gpa; + __u64 data_npages; + __u32 ret; + } ext_guest_req; }; };