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=-9.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 35BCBC3A5A9 for ; Mon, 4 May 2020 04:14:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 127B0206F1 for ; Mon, 4 May 2020 04:14:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="mPEo91Lt" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727892AbgEDEOd (ORCPT ); Mon, 4 May 2020 00:14:33 -0400 Received: from smtp-fw-6001.amazon.com ([52.95.48.154]:14448 "EHLO smtp-fw-6001.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727098AbgEDEOb (ORCPT ); Mon, 4 May 2020 00:14:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1588565672; x=1620101672; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version; bh=f42SAWEpwqudHXonrKA4kH+lQCUO1YP3xrO+LV4WQhs=; b=mPEo91Lt89JNo9I93heNsRvl9ZXaA5o7sxrc8J37OJfu97YXOp6XwkUQ p//q2CMtPMGwMoZ5u05RO6AkVuVhEHD4e/qGF9kyeTEpYbOeijMBGQ4h9 VtiJf8FRSn9N++n/Mdqup3wApIHZBLpyj9K0Fy/hWy+DiC50hGoGMh02p g=; IronPort-SDR: ZNvYprR0WaB4GObqt/IqNihXXySJzjGxi8xQL+tUwJybcIVys81ZtJ5VUOeG6urs2CuUGN/9Jv 653FroqRJGWQ== X-IronPort-AV: E=Sophos;i="5.73,350,1583193600"; d="scan'208";a="29830148" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-2b-4ff6265a.us-west-2.amazon.com) ([10.43.8.6]) by smtp-border-fw-out-6001.iad6.amazon.com with ESMTP; 04 May 2020 04:14:17 +0000 Received: from EX13MTAUWA001.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan3.pdx.amazon.com [10.170.41.166]) by email-inbound-relay-2b-4ff6265a.us-west-2.amazon.com (Postfix) with ESMTPS id 8EAD9A2702; Mon, 4 May 2020 04:14:15 +0000 (UTC) Received: from EX13D01UWA001.ant.amazon.com (10.43.160.60) by EX13MTAUWA001.ant.amazon.com (10.43.160.118) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Mon, 4 May 2020 04:14:06 +0000 Received: from EX13MTAUEA001.ant.amazon.com (10.43.61.82) by EX13d01UWA001.ant.amazon.com (10.43.160.60) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Mon, 4 May 2020 04:14:05 +0000 Received: from localhost (10.85.6.15) by mail-relay.amazon.com (10.43.61.243) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Mon, 4 May 2020 04:14:04 +0000 From: Balbir Singh To: , CC: , , , , , , , Balbir Singh Subject: [PATCH v5 6/6] Documentation: Add L1D flushing Documentation Date: Mon, 4 May 2020 14:13:43 +1000 Message-ID: <20200504041343.9651-7-sblbir@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200504041343.9651-1-sblbir@amazon.com> References: <20200504041343.9651-1-sblbir@amazon.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add documentation of l1d flushing, explain the need for the feature and how it can be used. Signed-off-by: Balbir Singh Reviewed-by: Kees Cook --- Documentation/admin-guide/hw-vuln/index.rst | 1 + .../admin-guide/hw-vuln/l1d_flush.rst | 40 +++++++++++++++++++ 2 files changed, 41 insertions(+) create mode 100644 Documentation/admin-guide/hw-vuln/l1d_flush.rst diff --git a/Documentation/admin-guide/hw-vuln/index.rst b/Documentation/admin-guide/hw-vuln/index.rst index 0795e3c2643f..35633b299d45 100644 --- a/Documentation/admin-guide/hw-vuln/index.rst +++ b/Documentation/admin-guide/hw-vuln/index.rst @@ -14,3 +14,4 @@ are configurable at compile, boot or run time. mds tsx_async_abort multihit.rst + l1d_flush diff --git a/Documentation/admin-guide/hw-vuln/l1d_flush.rst b/Documentation/admin-guide/hw-vuln/l1d_flush.rst new file mode 100644 index 000000000000..7d515b8c29f1 --- /dev/null +++ b/Documentation/admin-guide/hw-vuln/l1d_flush.rst @@ -0,0 +1,40 @@ +L1D Flushing for the paranoid +============================= + +With an increasing number of vulnerabilities being reported around data +leaks from L1D, a new user space mechanism to flush the L1D cache on +context switch is added to the kernel. This should help address +CVE-2020-0550 and for paranoid applications, keep them safe from any +yet to be discovered vulnerabilities, related to leaks from the L1D +cache. + +Tasks can opt in to this mechanism by using a prctl (implemented only +for x86 at the moment). + +Related CVES +------------ +At the present moment, the following CVEs can be addressed by this +mechanism + + ============= ======================== ================== + CVE-2020-0550 Improper Data Forwarding OS related aspects + ============= ======================== ================== + +Usage Guidelines +---------------- +Applications can call ``prctl(2)`` with one of these two arguments + +1. PR_SET_L1D_FLUSH - flush the L1D cache on context switch (out) +2. PR_GET_L1D_FLUSH - get the current state of the L1D cache flush, returns 1 + if set and 0 if not set. + +**NOTE**: The feature is disabled by default, applications to need to specifically +opt into the feature to enable it. + +Mitigation +---------- +When PR_SET_L1D_FLUSH is enabled for a task, on switching tasks (when +the address space changes), a flush of the L1D cache is performed for +the task when it leaves the CPU. If the underlying CPU supports L1D +flushing in hardware, the hardware mechanism is used, otherwise a software +fallback, similar to the mechanism used by L1TF is used. -- 2.17.1