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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 881CA1625709 for ; Mon, 30 Jul 2018 17:57:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 345AF208A1 for ; Mon, 30 Jul 2018 17:57:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 345AF208A1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732113AbeG3TdG (ORCPT ); Mon, 30 Jul 2018 15:33:06 -0400 Received: from mga17.intel.com ([192.55.52.151]:46737 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731549AbeG3TdG (ORCPT ); Mon, 30 Jul 2018 15:33:06 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 30 Jul 2018 10:56:58 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,422,1526367600"; d="scan'208";a="76808806" Received: from schen9-desk3.jf.intel.com (HELO [10.54.74.42]) ([10.54.74.42]) by fmsmga001.fm.intel.com with ESMTP; 30 Jul 2018 10:56:55 -0700 To: Jiri Kosina , Thomas Gleixner , Ingo Molnar , Konrad Rzeszutek Wilk , Borislav Petkov , David Woodhouse , Peter Zijlstra , Linus Torvalds Cc: linux-kernel@vger.kernel.org, Josh Poimboeuf , x86@kernel.org References: From: Tim Chen Openpgp: preference=signencrypt Autocrypt: addr=tim.c.chen@linux.intel.com; prefer-encrypt=mutual; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/26/2018 04:14 AM, Jiri Kosina wrote: > From: Jiri Kosina > > The article "Spectre Returns! Speculation Attacks using the Return Stack > Buffer" [1] describes two new (sub-)variants of spectrev2-like attack, > making use solely of the RSB contents even on CPUs that don't fallback to > BTB on RSB underflow (Skylake+). > > Mitigate userspace-userspace attacks by always unconditionally filling RSB on > context switch when generic spectrev2 mitigation has been enabled. > > [1] https://arxiv.org/pdf/1807.07940.pdf > > Reviewed-by: Josh Poimboeuf > Signed-off-by: Jiri Kosina > --- > > v1 -> v2: > > - Fixed typos/capatalization in SpectreRSB name > - Josh's Reviewed-by > > arch/x86/kernel/cpu/bugs.c | 38 +++++++------------------------------- > 1 file changed, 7 insertions(+), 31 deletions(-) > > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > index 5c0ea39311fe..bc8c43b22460 100644 > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -313,23 +313,6 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) > return cmd; > } > > -/* Check for Skylake-like CPUs (for RSB handling) */ > -static bool __init is_skylake_era(void) > -{ > - if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL && > - boot_cpu_data.x86 == 6) { > - switch (boot_cpu_data.x86_model) { > - case INTEL_FAM6_SKYLAKE_MOBILE: > - case INTEL_FAM6_SKYLAKE_DESKTOP: > - case INTEL_FAM6_SKYLAKE_X: > - case INTEL_FAM6_KABYLAKE_MOBILE: > - case INTEL_FAM6_KABYLAKE_DESKTOP: > - return true; > - } > - } > - return false; > -} > - > static void __init spectre_v2_select_mitigation(void) > { > enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline(); > @@ -390,22 +373,15 @@ static void __init spectre_v2_select_mitigation(void) > pr_info("%s\n", spectre_v2_strings[mode]); > > /* > - * If neither SMEP nor PTI are available, there is a risk of > - * hitting userspace addresses in the RSB after a context switch > - * from a shallow call stack to a deeper one. To prevent this fill > - * the entire RSB, even when using IBRS. > + * If spectre v2 protection has been enabled, unconditionally fill > + * RSB during a context switch; this protects against two independent > + * issues: > * > - * Skylake era CPUs have a separate issue with *underflow* of the > - * RSB, when they will predict 'ret' targets from the generic BTB. > - * The proper mitigation for this is IBRS. If IBRS is not supported > - * or deactivated in favour of retpolines the RSB fill on context > - * switch is required. > + * - RSB underflow (and switch to BTB) on Skylake+ > + * - SpectreRSB variant of spectre v2 on X86_BUG_SPECTRE_V2 CPUs > */ > - if ((!boot_cpu_has(X86_FEATURE_PTI) && > - !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) { > - setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW); > - pr_info("Spectre v2 mitigation: Filling RSB on context switch\n"); > - } > + setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW); > + pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n"); > > /* Initialize Indirect Branch Prediction Barrier if supported */ > if (boot_cpu_has(X86_FEATURE_IBPB)) { > Thanks for the patch. Looks good. Acked-by: Tim Chen Tim