| Message ID | 20210427170332.706287-1-aaronlewis@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4,1/2] kvm: x86: Allow userspace to handle emulation errors | expand |
On Tue, Apr 27, 2021 at 10:03 AM Aaron Lewis <aaronlewis@google.com> wrote: > > Add a fallback mechanism to the in-kernel instruction emulator that > allows userspace the opportunity to process an instruction the emulator > was unable to. When the in-kernel instruction emulator fails to process > an instruction it will either inject a #UD into the guest or exit to > userspace with exit reason KVM_INTERNAL_ERROR. This is because it does > not know how to proceed in an appropriate manner. This feature lets > userspace get involved to see if it can figure out a better path > forward. > > Signed-off-by: Aaron Lewis <aaronlewis@google.com> ... > +static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu) > +{ > + struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt; > + u64 insn_size = ctxt->fetch.end - ctxt->fetch.data; > + struct kvm_run *run = vcpu->run; > + const u64 max_insn_size = 15; Nit: insn_size and max_insn_size could both be just unsigned int. > + run->exit_reason = KVM_EXIT_INTERNAL_ERROR; > + run->emulation_failure.suberror = KVM_INTERNAL_ERROR_EMULATION; > + run->emulation_failure.ndata = 0; > + run->emulation_failure.flags = 0; > + > + if (insn_size) { > + run->emulation_failure.ndata = 3; > + run->emulation_failure.flags |= > + KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES; > + run->emulation_failure.insn_size = insn_size; > + memset(run->emulation_failure.insn_bytes, 0x90, max_insn_size); > + memcpy(run->emulation_failure.insn_bytes, > + ctxt->fetch.data, insn_size); It's tempting to check that insn_size doesn't exceed 15, but I'm sure we all trust the emulator. > + } > +} > + > static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type) > { > + struct kvm *kvm = vcpu->kvm; > + > ++vcpu->stat.insn_emulation_fail; > trace_kvm_emulate_insn_failed(vcpu); > > @@ -7129,10 +7159,9 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type) > return 1; > } > > - if (emulation_type & EMULTYPE_SKIP) { > - vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR; > - vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION; > - vcpu->run->internal.ndata = 0; > + if (kvm->arch.exit_on_emulation_error || > + (emulation_type & EMULTYPE_SKIP)) { > + prepare_emulation_failure_exit(vcpu); > return 0; > } > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index f6afee209620..87009222c20c 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -279,6 +279,9 @@ struct kvm_xen_exit { > /* Encounter unexpected vm-exit reason */ > #define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON 4 > > +/* Flags that describe what fields in emulation_failure hold valid data. */ > +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0) > + > /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */ > struct kvm_run { > /* in */ > @@ -382,6 +385,25 @@ struct kvm_run { > __u32 ndata; > __u64 data[16]; > } internal; > + /* > + * KVM_INTERNAL_ERROR_EMULATION > + * > + * "struct emulation_failure" is an overlay of "struct internal" > + * that is used for the KVM_INTERNAL_ERROR_EMULATION sub-type of > + * KVM_EXIT_INTERNAL_ERROR. Note, unlike other internal error > + * sub-types, this struct is ABI! It also needs to be backwards > + * compabile with "struct internal". Take special care that > + * "ndata" is correct, that new fields are enumerated in "flags", > + * and that each flag enumerates fields that are 64-bit aligned > + * and sized (so that ndata+internal.data[] is valid/accurate). > + */ > + struct { > + __u32 suberror; > + __u32 ndata; > + __u64 flags; > + __u8 insn_size; > + __u8 insn_bytes[15]; > + } emulation_failure; > /* KVM_EXIT_OSI */ > struct { > __u64 gprs[32]; > @@ -1078,6 +1100,7 @@ struct kvm_ppc_resize_hpt { > #define KVM_CAP_DIRTY_LOG_RING 192 > #define KVM_CAP_X86_BUS_LOCK_EXIT 193 > #define KVM_CAP_PPC_DAWR1 194 > +#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 195 > > #ifdef KVM_CAP_IRQ_ROUTING > > diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h > index f6afee209620..87009222c20c 100644 > --- a/tools/include/uapi/linux/kvm.h > +++ b/tools/include/uapi/linux/kvm.h > @@ -279,6 +279,9 @@ struct kvm_xen_exit { > /* Encounter unexpected vm-exit reason */ > #define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON 4 > > +/* Flags that describe what fields in emulation_failure hold valid data. */ > +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0) > + > /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */ > struct kvm_run { > /* in */ > @@ -382,6 +385,25 @@ struct kvm_run { > __u32 ndata; > __u64 data[16]; > } internal; > + /* > + * KVM_INTERNAL_ERROR_EMULATION > + * > + * "struct emulation_failure" is an overlay of "struct internal" > + * that is used for the KVM_INTERNAL_ERROR_EMULATION sub-type of > + * KVM_EXIT_INTERNAL_ERROR. Note, unlike other internal error > + * sub-types, this struct is ABI! It also needs to be backwards > + * compabile with "struct internal". Take special care that > + * "ndata" is correct, that new fields are enumerated in "flags", > + * and that each flag enumerates fields that are 64-bit aligned > + * and sized (so that ndata+internal.data[] is valid/accurate). > + */ > + struct { > + __u32 suberror; > + __u32 ndata; > + __u64 flags; > + __u8 insn_size; > + __u8 insn_bytes[15]; > + } emulation_failure; > /* KVM_EXIT_OSI */ > struct { > __u64 gprs[32]; > @@ -1078,6 +1100,7 @@ struct kvm_ppc_resize_hpt { > #define KVM_CAP_DIRTY_LOG_RING 192 > #define KVM_CAP_X86_BUS_LOCK_EXIT 193 > #define KVM_CAP_PPC_DAWR1 194 > +#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 195 > > #ifdef KVM_CAP_IRQ_ROUTING > > -- > 2.31.1.498.g6c1eba8ee3d-goog >
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 307f2fcf1b02..6ae57fdf3a56 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6233,6 +6233,24 @@ KVM_RUN_BUS_LOCK flag is used to distinguish between them. This capability can be used to check / enable 2nd DAWR feature provided by POWER10 processor. +7.24 KVM_CAP_EXIT_ON_EMULATION_FAILURE +-------------------------------------- + +:Architectures: x86 +:Parameters: args[0] whether the feature should be enabled or not + +When this capability is enabled the in-kernel instruction emulator packs +the exit struct of KVM_INTERNAL_ERROR with the instrution length and +instruction bytes when an error occurs while emulating an instruction. This +will also happen when the emulation type is set to EMULTYPE_SKIP, but with this +capability enabled this becomes the default behavior regarless of how the +emulation type is set unless it is a VMware #GP; in that case a #GP is injected +and KVM does not exit to userspace. + +When this capability is enabled use the emulation_failure struct instead of the +internal struct for the exit struct. They have the same layout, but the +emulation_failure struct matches the content better. + 8. Other capabilities. ====================== diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 3768819693e5..07235d08e976 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1049,6 +1049,12 @@ struct kvm_arch { bool exception_payload_enabled; bool bus_lock_detection_enabled; + /* + * If exit_on_emulation_error is set, and the in-kernel instruction + * emulator fails to emulate an instruction, allow userspace + * the opportunity to look at it. + */ + bool exit_on_emulation_error; /* Deflect RDMSR and WRMSR to user space when they trigger a #GP */ u32 user_space_msr_mask; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index eca63625aee4..ef7d07d60b34 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3771,6 +3771,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_X86_USER_SPACE_MSR: case KVM_CAP_X86_MSR_FILTER: case KVM_CAP_ENFORCE_PV_FEATURE_CPUID: + case KVM_CAP_EXIT_ON_EMULATION_FAILURE: r = 1; break; #ifdef CONFIG_KVM_XEN @@ -5357,6 +5358,10 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, kvm->arch.bus_lock_detection_enabled = true; r = 0; break; + case KVM_CAP_EXIT_ON_EMULATION_FAILURE: + kvm->arch.exit_on_emulation_error = cap->args[0]; + r = 0; + break; default: r = -EINVAL; break; @@ -7119,8 +7124,33 @@ void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip) } EXPORT_SYMBOL_GPL(kvm_inject_realmode_interrupt); +static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu) +{ + struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt; + u64 insn_size = ctxt->fetch.end - ctxt->fetch.data; + struct kvm_run *run = vcpu->run; + const u64 max_insn_size = 15; + + run->exit_reason = KVM_EXIT_INTERNAL_ERROR; + run->emulation_failure.suberror = KVM_INTERNAL_ERROR_EMULATION; + run->emulation_failure.ndata = 0; + run->emulation_failure.flags = 0; + + if (insn_size) { + run->emulation_failure.ndata = 3; + run->emulation_failure.flags |= + KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES; + run->emulation_failure.insn_size = insn_size; + memset(run->emulation_failure.insn_bytes, 0x90, max_insn_size); + memcpy(run->emulation_failure.insn_bytes, + ctxt->fetch.data, insn_size); + } +} + static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type) { + struct kvm *kvm = vcpu->kvm; + ++vcpu->stat.insn_emulation_fail; trace_kvm_emulate_insn_failed(vcpu); @@ -7129,10 +7159,9 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type) return 1; } - if (emulation_type & EMULTYPE_SKIP) { - vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR; - vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION; - vcpu->run->internal.ndata = 0; + if (kvm->arch.exit_on_emulation_error || + (emulation_type & EMULTYPE_SKIP)) { + prepare_emulation_failure_exit(vcpu); return 0; } diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index f6afee209620..87009222c20c 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -279,6 +279,9 @@ struct kvm_xen_exit { /* Encounter unexpected vm-exit reason */ #define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON 4 +/* Flags that describe what fields in emulation_failure hold valid data. */ +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0) + /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */ struct kvm_run { /* in */ @@ -382,6 +385,25 @@ struct kvm_run { __u32 ndata; __u64 data[16]; } internal; + /* + * KVM_INTERNAL_ERROR_EMULATION + * + * "struct emulation_failure" is an overlay of "struct internal" + * that is used for the KVM_INTERNAL_ERROR_EMULATION sub-type of + * KVM_EXIT_INTERNAL_ERROR. Note, unlike other internal error + * sub-types, this struct is ABI! It also needs to be backwards + * compabile with "struct internal". Take special care that + * "ndata" is correct, that new fields are enumerated in "flags", + * and that each flag enumerates fields that are 64-bit aligned + * and sized (so that ndata+internal.data[] is valid/accurate). + */ + struct { + __u32 suberror; + __u32 ndata; + __u64 flags; + __u8 insn_size; + __u8 insn_bytes[15]; + } emulation_failure; /* KVM_EXIT_OSI */ struct { __u64 gprs[32]; @@ -1078,6 +1100,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_DIRTY_LOG_RING 192 #define KVM_CAP_X86_BUS_LOCK_EXIT 193 #define KVM_CAP_PPC_DAWR1 194 +#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 195 #ifdef KVM_CAP_IRQ_ROUTING diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h index f6afee209620..87009222c20c 100644 --- a/tools/include/uapi/linux/kvm.h +++ b/tools/include/uapi/linux/kvm.h @@ -279,6 +279,9 @@ struct kvm_xen_exit { /* Encounter unexpected vm-exit reason */ #define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON 4 +/* Flags that describe what fields in emulation_failure hold valid data. */ +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0) + /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */ struct kvm_run { /* in */ @@ -382,6 +385,25 @@ struct kvm_run { __u32 ndata; __u64 data[16]; } internal; + /* + * KVM_INTERNAL_ERROR_EMULATION + * + * "struct emulation_failure" is an overlay of "struct internal" + * that is used for the KVM_INTERNAL_ERROR_EMULATION sub-type of + * KVM_EXIT_INTERNAL_ERROR. Note, unlike other internal error + * sub-types, this struct is ABI! It also needs to be backwards + * compabile with "struct internal". Take special care that + * "ndata" is correct, that new fields are enumerated in "flags", + * and that each flag enumerates fields that are 64-bit aligned + * and sized (so that ndata+internal.data[] is valid/accurate). + */ + struct { + __u32 suberror; + __u32 ndata; + __u64 flags; + __u8 insn_size; + __u8 insn_bytes[15]; + } emulation_failure; /* KVM_EXIT_OSI */ struct { __u64 gprs[32]; @@ -1078,6 +1100,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_DIRTY_LOG_RING 192 #define KVM_CAP_X86_BUS_LOCK_EXIT 193 #define KVM_CAP_PPC_DAWR1 194 +#define KVM_CAP_EXIT_ON_EMULATION_FAILURE 195 #ifdef KVM_CAP_IRQ_ROUTING
Add a fallback mechanism to the in-kernel instruction emulator that allows userspace the opportunity to process an instruction the emulator was unable to. When the in-kernel instruction emulator fails to process an instruction it will either inject a #UD into the guest or exit to userspace with exit reason KVM_INTERNAL_ERROR. This is because it does not know how to proceed in an appropriate manner. This feature lets userspace get involved to see if it can figure out a better path forward. Signed-off-by: Aaron Lewis <aaronlewis@google.com> --- Documentation/virt/kvm/api.rst | 18 ++++++++++++++++ arch/x86/include/asm/kvm_host.h | 6 ++++++ arch/x86/kvm/x86.c | 37 +++++++++++++++++++++++++++++---- include/uapi/linux/kvm.h | 23 ++++++++++++++++++++ tools/include/uapi/linux/kvm.h | 23 ++++++++++++++++++++ 5 files changed, 103 insertions(+), 4 deletions(-)