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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=no 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 E7DF0C28CBC for ; Sat, 9 May 2020 17:37:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C1A272192A for ; Sat, 9 May 2020 17:37:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589045821; bh=9853mSKZsku5U79WiBkvplqTJllbx6OfEy4JNS5F/d0=; h=From:To:Cc:Subject:Date:List-ID:From; b=D5tK4Zt1SEUUDVWrjEZH6EBFO1/AXxPd5rMGgoS9TL/ce6tkPc+67uK6DWA88iRe4 yw7Fhco7Wg+qA3D0RMin7Z8TwaIBFpIvojSH9xjEqsP1AMmRg/hCKfQhX7R3Q1Dy/o 0V8SDJebNi04Hks2CQDjc5rogo96W/gdVKw4E9fk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728275AbgEIRhB (ORCPT ); Sat, 9 May 2020 13:37:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:54200 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726214AbgEIRhA (ORCPT ); Sat, 9 May 2020 13:37:00 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B122A20A8B; Sat, 9 May 2020 17:36:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589045819; bh=9853mSKZsku5U79WiBkvplqTJllbx6OfEy4JNS5F/d0=; h=From:To:Cc:Subject:Date:From; b=OrqzLnS6QyFGGzjQ0Hn4wYuE4HoWmIkWcgqYjwzwzvheUm9ZjCz/DU2H+pFLXi9sf 2dXRbfGMIVzq/6BqeSLCN21CVMUXkvyE8uCtZODFkBevOvYpwugQuOvD4nU3x1s4kE DV2O8HFU6Ngm70YVm3jepYxP1ryy9BAuukxMHNiw= From: Sasha Levin To: linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, luto@kernel.org Cc: hpa@zytor.com, dave.hansen@intel.com, tony.luck@intel.com, ak@linux.intel.com, ravi.v.shankar@intel.com, chang.seok.bae@intel.com, Sasha Levin Subject: [PATCH v11 00/18] Enable FSGSBASE instructions Date: Sat, 9 May 2020 13:36:37 -0400 Message-Id: <20200509173655.13977-1-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Benefits: Currently a user process that wishes to read or write the FS/GS base must make a system call. But recent X86 processors have added new instructions for use in 64-bit mode that allow direct access to the FS and GS segment base addresses. The operating system controls whether applications can use these instructions with a %cr4 control bit. In addition to benefits to applications, performance improvements to the OS context switch code are possible by making use of these instructions. A third party reported out promising performance numbers out of their initial benchmarking of the previous version of this patch series [9]. Enablement check: The kernel provides information about the enabled state of FSGSBASE to applications using the ELF_AUX vector. If the HWCAP2_FSGSBASE bit is set in the AUX vector, the kernel has FSGSBASE instructions enabled and applications can use them. Kernel changes: Major changes made in the kernel are in context switch, paranoid path, and ptrace. In a context switch, a task's FS/GS base will be secured regardless of its selector. In the paranoid path, GS base is unconditionally overwritten to the kernel GS base on entry and the original GS base is restored on exit. Ptrace includes divergence of FS/GS index and base values. Security: For mitigating the Spectre v1 SWAPGS issue, LFENCE instructions were added on most kernel entries. Those patches are dependent on previous behaviors that users couldn't load a kernel address into the GS base. These patches change that assumption since the user can load any address into GS base. The changes to the kernel entry path in this patch series take account of the SWAPGS issue. Changes from v10: - Rewrite the commit message for patch #1. - Document communication/acks from userspace projects that are potentially affected by this. Andi Kleen (2): x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Andy Lutomirski (4): x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE x86/entry/64: Clean up paranoid exit x86/fsgsbase/64: Use FSGSBASE in switch_to() if available x86/fsgsbase/64: Enable FSGSBASE on 64bit by default and add a chicken bit Chang S. Bae (9): x86/ptrace: Prevent ptrace from clearing the FS/GS selector selftests/x86/fsgsbase: Test GS selector on ptracer-induced GS base write x86/entry/64: Switch CR3 before SWAPGS in paranoid entry x86/entry/64: Introduce the FIND_PERCPU_BASE macro x86/entry/64: Handle FSGSBASE enabled paranoid entry/exit x86/entry/64: Document GSBASE handling in the paranoid path x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions x86/fsgsbase/64: Use FSGSBASE instructions on thread copy and ptrace selftests/x86/fsgsbase: Test ptracer-induced GS base write with FSGSBASE Sasha Levin (1): x86/fsgsbase/64: move save_fsgs to header file Thomas Gleixner (1): Documentation/x86/64: Add documentation for GS/FS addressing mode Tony Luck (1): x86/speculation/swapgs: Check FSGSBASE in enabling SWAPGS mitigation .../admin-guide/kernel-parameters.txt | 2 + Documentation/x86/entry_64.rst | 9 + Documentation/x86/x86_64/fsgs.rst | 199 ++++++++++++++++++ Documentation/x86/x86_64/index.rst | 1 + arch/x86/entry/calling.h | 40 ++++ arch/x86/entry/entry_64.S | 131 +++++++++--- arch/x86/include/asm/fsgsbase.h | 45 +++- arch/x86/include/asm/inst.h | 15 ++ arch/x86/include/uapi/asm/hwcap2.h | 3 + arch/x86/kernel/cpu/bugs.c | 6 +- arch/x86/kernel/cpu/common.c | 22 ++ arch/x86/kernel/process.c | 10 +- arch/x86/kernel/process.h | 68 ++++++ arch/x86/kernel/process_64.c | 142 +++++++------ arch/x86/kernel/ptrace.c | 17 +- tools/testing/selftests/x86/fsgsbase.c | 24 ++- 16 files changed, 605 insertions(+), 129 deletions(-) create mode 100644 Documentation/x86/x86_64/fsgs.rst -- 2.20.1