From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 64B47C433B4 for ; Wed, 21 Apr 2021 14:03:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 38E5F6144B for ; Wed, 21 Apr 2021 14:03:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243179AbhDUODi (ORCPT ); Wed, 21 Apr 2021 10:03:38 -0400 Received: from forward5-smtp.messagingengine.com ([66.111.4.239]:49843 "EHLO forward5-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236913AbhDUODh (ORCPT ); Wed, 21 Apr 2021 10:03:37 -0400 Received: from compute4.internal (compute4.nyi.internal [10.202.2.44]) by mailforward.nyi.internal (Postfix) with ESMTP id DF9AC1941B3B; Wed, 21 Apr 2021 10:03:03 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute4.internal (MEProxy); Wed, 21 Apr 2021 10:03:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to:x-me-proxy :x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm2; bh=t1OE9Q B/8TDw7pwOgGnWyT/eTvOjkdzgd792YLN1RiM=; b=cy+qZI4v7vdKDj/ZKd0c+U fajRgkAFywS1co1IKSbY3dD96UMKRplyiegyXI9uinQAP8dNe+Cyawp0dXc6cKYq 6/or6wTWvJu5qNKUg2nLvYWXVzlvKIjGLfzfS+SdNIbJJ/eB60+JAuzLmJQXi+O+ fJKYD+DOTrHJPIfIG31+eYLSCVA2QRxRwnHvvGBvWAZmSaw6CZm7HvkaW0sGfQa0 dEsWO/o0WniyS8Vltu6z78vY6/v0OGCXo6KfOYfi1vWgKLYkL9DzMZv+TZh1UVbD OwPYQpLyZwTpAHmOeew4zSL9ppTd2DZRZJBOLFP5a98lFz2A99cLL2PL3bnfrnXw == X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeduledrvddtkedgjedvucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepvffujghfhfffkfggtgesthdtredttddttdenucfhrhhomhepffgrvhhiugcu gfgumhhonhgushhonhcuoegumhgvsegumhgvrdhorhhgqeenucggtffrrghtthgvrhhnpe fhkeeguedtvdegffffteehjedvjeeitefgfefgffdugeffffegudehgeetgeelkeenucfk phepkedurddukeejrddviedrvdefkeenucevlhhushhtvghrufhiiigvpedtnecurfgrrh grmhepmhgrihhlfhhrohhmpegumhgvsegumhgvrdhorhhg X-ME-Proxy: Received: from disaster-area.hh.sledj.net (disaster-area.hh.sledj.net [81.187.26.238]) by mail.messagingengine.com (Postfix) with ESMTPA id CB03324006B; Wed, 21 Apr 2021 10:03:02 -0400 (EDT) Received: from localhost (disaster-area.hh.sledj.net [local]) by disaster-area.hh.sledj.net (OpenSMTPD) with ESMTPA id 260fd885; Wed, 21 Apr 2021 14:03:01 +0000 (UTC) To: Aaron Lewis , seanjc@google.com Cc: jmattson@google.com, kvm@vger.kernel.org, Aaron Lewis Subject: Re: [PATCH v2 1/2] kvm: x86: Allow userspace to handle emulation errors In-Reply-To: <20210421122833.3881993-1-aaronlewis@google.com> References: <20210421122833.3881993-1-aaronlewis@google.com> X-HGTTG: zarquon From: David Edmondson X-Now-Playing: Four Tet - Rounds: Hands Date: Wed, 21 Apr 2021 15:03:01 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wednesday, 2021-04-21 at 05:28:32 -07, Aaron Lewis 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 > --- > Documentation/virt/kvm/api.rst | 19 ++++++++++++++++++ > arch/x86/include/asm/kvm_host.h | 6 ++++++ > arch/x86/kvm/x86.c | 35 +++++++++++++++++++++++++++++---- > include/uapi/linux/kvm.h | 23 ++++++++++++++++++++++ > tools/include/uapi/linux/kvm.h | 23 ++++++++++++++++++++++ > 5 files changed, 102 insertions(+), 4 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index 307f2fcf1b02..fe6c3f1cae7e 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -6233,6 +6233,25 @@ 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 > + > +With this capability enabled, the in-kernel instruction emulator packs the exit > +struct of KVM_INTERNAL_ERROR with the instruction length and instruction bytes > +when an error occurs while emulating an instruction. This allows userspace to > +then take a look at the instruction and see if it is able to handle it more > +gracefully than the in-kernel emulator. It will do so without KVM_CAP_EXIT_ON_EMULATION_FAILURE enabled in this set of changes. That is, the payload can be present irrespective of the capability being enabled. > +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. > + > +It is noted that KVM still exits on certain types (skip) even if this capability > +is not enabled, and KVM will never exit if VMware #GP emulation fails. > + > 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..9cdfb7fbead5 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 +7124,31 @@ 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; > + > + Unnecessary extra blank line here... > + 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; ...that I would move here, but your call :-) > + 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; > + memcpy(run->emulation_failure.insn_bytes, > + ctxt->fetch.data, sizeof(ctxt->fetch.data)); We're relying on the fact that insn_bytes is at least as large as fetch.data, which is fine, but worth an assertion? "Leaking" irrelevant bytes here also seems bad, but I can't immediately see a problem as a result. > + } > +} > + > 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 +7157,9 @@ 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..d7d109e6998f 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..d7d109e6998f 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 */ Extra space at the end. > +#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 dme. -- Everyone I know, goes away in the end.