From patchwork Wed Feb 14 13:44:32 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Woodhouse, David" X-Patchwork-Id: 10218903 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id A1D7A602CB for ; Wed, 14 Feb 2018 13:45:17 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 905F228FAE for ; Wed, 14 Feb 2018 13:45:17 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 84A4328FDE; Wed, 14 Feb 2018 13:45:17 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id AC2A328FAE for ; Wed, 14 Feb 2018 13:45:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030506AbeBNNo5 (ORCPT ); Wed, 14 Feb 2018 08:44:57 -0500 Received: from smtp-fw-6002.amazon.com ([52.95.49.90]:1054 "EHLO smtp-fw-6002.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030487AbeBNNoy (ORCPT ); Wed, 14 Feb 2018 08:44:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.co.uk; i=@amazon.co.uk; q=dns/txt; s=amazon201209; t=1518615894; x=1550151894; h=from:to:subject:date:message-id:in-reply-to:references; bh=tJoLPl69gdctK9FMFjuD/Y73lTQmypIJ5LVnkb4bhng=; b=QI9StwYDJaLV8cgc8oMzHCY6iedWexbUQ1lmG7HjzRoRU/ASslD48Jjb teUD/Zn7SC1fmbqSTEvC5vErt8PjXzoyhy+/aai6ewxEaE2vtSWnZM2k/ N1gZ/7pgzJ9GfSenCqBdp9Mrh5nq0MY58cNlTTvH8+M35Y+QI6wKmZD3I 8=; X-IronPort-AV: E=Sophos;i="5.46,512,1511827200"; d="scan'208";a="332036398" Received: from iad6-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-1d-98acfc19.us-east-1.amazon.com) ([10.124.125.6]) by smtp-border-fw-out-6002.iad6.amazon.com with ESMTP/TLS/DHE-RSA-AES256-SHA; 14 Feb 2018 13:44:53 +0000 Received: from uc8d3ff76b9bc5848a9cc.ant.amazon.com (iad1-ws-svc-lb91-vlan3.amazon.com [10.0.103.150]) by email-inbound-relay-1d-98acfc19.us-east-1.amazon.com (8.14.7/8.14.7) with ESMTP id w1EDig9o102929 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 14 Feb 2018 13:44:44 GMT Received: from uc8d3ff76b9bc5848a9cc.ant.amazon.com (localhost [127.0.0.1]) by uc8d3ff76b9bc5848a9cc.ant.amazon.com (8.15.2/8.15.2/Debian-3) with ESMTP id w1EDifQO014268; Wed, 14 Feb 2018 13:44:41 GMT Received: (from dwmw@localhost) by uc8d3ff76b9bc5848a9cc.ant.amazon.com (8.15.2/8.15.2/Submit) id w1EDifDI014264; Wed, 14 Feb 2018 13:44:41 GMT From: David Woodhouse To: tglx@linutronix.de, karahmed@amazon.de, x86@kernel.org, kvm@vger.kernel.org, torvalds@linux-foundation.org, pbonzini@redhat.com, linux-kernel@vger.kernel.org, bp@alien8.de, peterz@infradead.org, jmattson@google.com, rkrcmar@redhat.com, arjan.van.de.ven@intel.com, dave.hansen@intel.com, mingo@kernel.org Subject: [PATCH 2/4] x86/speculation: Support "Enhanced IBRS" on future CPUs Date: Wed, 14 Feb 2018 13:44:32 +0000 Message-Id: <1518615874-13806-3-git-send-email-dwmw@amazon.co.uk> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1518615874-13806-1-git-send-email-dwmw@amazon.co.uk> References: <1518615874-13806-1-git-send-email-dwmw@amazon.co.uk> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The original IBRS hack in microcode is horribly slow. For the next generation of CPUs, as a stopgap until we get a proper fix, Intel promise an "Enhanced IBRS" which will be fast. The assumption is that predictions in the BTB/RSB will be tagged with the VMX mode and ring that they were learned in, and thus the CPU will avoid consuming unsafe predictions without a performance penalty. Intel's documentation says that it is still required to set the IBRS bit in the SPEC_CTRL MSR and ensure that it remains set. Cope with this by trapping and emulating *all* access to SPEC_CTRL from KVM guests when the IBRS_ALL feature is present, so it can never be turned off. Guests who see IBRS_ALL should never do anything except turn it on at boot anyway. And if they didn't know about IBRS_ALL and they keep frobbing IBRS on every kernel entry/exit... well the vmexit for a no-op is probably going to be faster than they were expecting anyway, so they'll live. Signed-off-by: David Woodhouse Acked-by: Arjan van de Ven --- arch/x86/include/asm/nospec-branch.h | 9 ++++++++- arch/x86/kernel/cpu/bugs.c | 16 ++++++++++++++-- arch/x86/kvm/vmx.c | 31 +++++++++++++++++++------------ 3 files changed, 41 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 0995c6a..34cbce3 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -141,9 +141,16 @@ enum spectre_v2_mitigation { SPECTRE_V2_RETPOLINE_MINIMAL_AMD, SPECTRE_V2_RETPOLINE_GENERIC, SPECTRE_V2_RETPOLINE_AMD, - SPECTRE_V2_IBRS, + SPECTRE_V2_IBRS_ALL, }; +extern enum spectre_v2_mitigation spectre_v2_enabled; + +static inline bool spectre_v2_ibrs_all(void) +{ + return spectre_v2_enabled == SPECTRE_V2_IBRS_ALL; +} + extern char __indirect_thunk_start[]; extern char __indirect_thunk_end[]; diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index bfca937..eefd900 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -88,12 +88,13 @@ static const char *spectre_v2_strings[] = { [SPECTRE_V2_RETPOLINE_MINIMAL_AMD] = "Vulnerable: Minimal AMD ASM retpoline", [SPECTRE_V2_RETPOLINE_GENERIC] = "Mitigation: Full generic retpoline", [SPECTRE_V2_RETPOLINE_AMD] = "Mitigation: Full AMD retpoline", + [SPECTRE_V2_IBRS_ALL] = "Mitigation: Enhanced IBRS", }; #undef pr_fmt #define pr_fmt(fmt) "Spectre V2 : " fmt -static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE; +enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE; #ifdef RETPOLINE static bool spectre_v2_bad_module; @@ -237,6 +238,16 @@ static void __init spectre_v2_select_mitigation(void) case SPECTRE_V2_CMD_FORCE: case SPECTRE_V2_CMD_AUTO: + if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES)) { + u64 ia32_cap = 0; + + rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap); + if (ia32_cap & ARCH_CAP_IBRS_ALL) { + mode = SPECTRE_V2_IBRS_ALL; + wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_IBRS); + goto ibrs_all; + } + } if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_auto; break; @@ -274,6 +285,7 @@ static void __init spectre_v2_select_mitigation(void) setup_force_cpu_cap(X86_FEATURE_RETPOLINE); } + ibrs_all: spectre_v2_enabled = mode; pr_info("%s\n", spectre_v2_strings[mode]); @@ -305,7 +317,7 @@ static void __init spectre_v2_select_mitigation(void) * Retpoline means the kernel is safe because it has no indirect * branches. But firmware isn't, so use IBRS to protect that. */ - if (boot_cpu_has(X86_FEATURE_IBRS)) { + if (mode != SPECTRE_V2_IBRS_ALL && boot_cpu_has(X86_FEATURE_IBRS)) { setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW); pr_info("Enabling Restricted Speculation for firmware calls\n"); } diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 91e3539..62ad7e3 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -3419,13 +3419,14 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) vmx->spec_ctrl = data; - if (!data) + if (!data && !spectre_v2_ibrs_all()) break; /* * For non-nested: * When it's written (to non-zero) for the first time, pass - * it through. + * it through unless we have IBRS_ALL and it should just be + * set for ever. * * For nested: * The handling of the MSR bitmap for L2 guests is done in @@ -9441,7 +9442,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) * is no need to worry about the conditional branch over the wrmsr * being speculatively taken. */ - if (vmx->spec_ctrl) + if (!spectre_v2_ibrs_all() && vmx->spec_ctrl) wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl); vmx->__launched = vmx->loaded_vmcs->launched; @@ -9563,11 +9564,12 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) ); /* - * We do not use IBRS in the kernel. If this vCPU has used the - * SPEC_CTRL MSR it may have left it on; save the value and - * turn it off. This is much more efficient than blindly adding - * it to the atomic save/restore list. Especially as the former - * (Saving guest MSRs on vmexit) doesn't even exist in KVM. + * Without IBRS_ALL, we do not use IBRS in the kernel. If this + * vCPU has used the SPEC_CTRL MSR it may have left it on; + * save the value and turn it off. This is much more efficient + * than blindly adding it to the atomic save/restore list. + * Especially as the former (saving guest MSRs on vmexit) + * doesn't even exist in KVM. * * For non-nested case: * If the L01 MSR bitmap does not intercept the MSR, then we need to @@ -9576,12 +9578,17 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) * For nested case: * If the L02 MSR bitmap does not intercept the MSR, then we need to * save it. + * + * If IBRS_ALL is present then the whole thing is a no-op fiction + * for guests and every access is trapped, so do nothing. */ - if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)) - rdmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl); + if (!spectre_v2_ibrs_all()) { + if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)) + rdmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl); - if (vmx->spec_ctrl) - wrmsrl(MSR_IA32_SPEC_CTRL, 0); + if (vmx->spec_ctrl) + wrmsrl(MSR_IA32_SPEC_CTRL, 0); + } /* Eliminate branch target predictions from guest mode */ vmexit_fill_RSB();