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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 F2C97C54E4A for ; Mon, 11 May 2020 04:53:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D04DF2063A for ; Mon, 11 May 2020 04:53:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589172819; bh=3HxCBk+i1/xuyraquCNdCuSz2+rSr/9JEZRSASx8d8g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=jJ4PpQ0d/DEl8ztJfs7piL10dPoqS0cQQTLRKiI1mdxmZbP4e/NDW+jMIkzmurYkZ SWewfTE/SGV6sZ1sBHu5MU4WUDZwxYcxUc2PES/LL3Y1h98bmsrMfYwkCGztIyyjsr KjU7DWM2w8sThhQScbDRGmTc7MGH3GJbQJWdou7U= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728501AbgEKExi (ORCPT ); Mon, 11 May 2020 00:53:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:37360 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728402AbgEKExe (ORCPT ); Mon, 11 May 2020 00:53:34 -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 97AFD208CA; Mon, 11 May 2020 04:53:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589172813; bh=3HxCBk+i1/xuyraquCNdCuSz2+rSr/9JEZRSASx8d8g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HtzEeJ/sLW7i7ykoJ5YdZfZX6ZUKvdyUdqWrzAu+6aP/E3sX9iNpLwKK1USP7pmPZ ckEigyHhNLGGZ0NeWbigP07G1cOntkoOklzmgJatM9bB1p6IhF8avMAaPyKIAGF0KZ M8rOGIw05V65fD9JZ0Rt0SnQI01G+zj3l1NA5Ra0= 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 , Vegard Nossum Subject: [PATCH v12 05/18] x86/entry/64: Switch CR3 before SWAPGS in paranoid entry Date: Mon, 11 May 2020 00:52:58 -0400 Message-Id: <20200511045311.4785-6-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200511045311.4785-1-sashal@kernel.org> References: <20200511045311.4785-1-sashal@kernel.org> 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 From: "Chang S. Bae" When FSGSBASE is enabled, the GS base handling in paranoid entry will need to retrieve the kernel GS base which requires that the kernel page table is active. As the CR3 switch to the kernel page tables (PTI is active) does not depend on kernel GS base, move the CR3 switch in front of the GS base handling. Comment the EBX content while at it. No functional change. Signed-off-by: Chang S. Bae Signed-off-by: Sasha Levin Reviewed-by: Tony Luck Cc: Thomas Gleixner Cc: Borislav Petkov Cc: Andy Lutomirski Cc: H. Peter Anvin Cc: Dave Hansen Cc: Tony Luck Cc: Andi Kleen Cc: Vegard Nossum --- arch/x86/entry/entry_64.S | 31 +++++++++++++++++++------------ 1 file changed, 19 insertions(+), 12 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 0da56e6791b73..3ac1313724eaa 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1220,15 +1220,7 @@ SYM_CODE_START_LOCAL(paranoid_entry) cld PUSH_AND_CLEAR_REGS save_ret=1 ENCODE_FRAME_POINTER 8 - movl $1, %ebx - movl $MSR_GS_BASE, %ecx - rdmsr - testl %edx, %edx - js 1f /* negative -> in kernel */ - SWAPGS - xorl %ebx, %ebx -1: /* * Always stash CR3 in %r14. This value will be restored, * verbatim, at exit. Needed if paranoid_entry interrupted @@ -1238,16 +1230,31 @@ SYM_CODE_START_LOCAL(paranoid_entry) * This is also why CS (stashed in the "iret frame" by the * hardware at entry) can not be used: this may be a return * to kernel code, but with a user CR3 value. + * + * Switching CR3 does not depend on kernel GS base so it can + * be done before switching to the kernel GS base. This is + * required for FSGSBASE because the kernel GS base has to + * be retrieved from a kernel internal table. */ SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14 + /* EBX = 1 -> kernel GSBASE active, no restore required */ + movl $1, %ebx /* - * The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro doesn't do an - * unconditional CR3 write, even in the PTI case. So do an lfence - * to prevent GS speculation, regardless of whether PTI is enabled. + * The kernel-enforced convention is a negative GS base indicates + * a kernel value. No SWAPGS needed on entry and exit. */ - FENCE_SWAPGS_KERNEL_ENTRY + movl $MSR_GS_BASE, %ecx + rdmsr + testl %edx, %edx + jns .Lparanoid_entry_swapgs + ret +.Lparanoid_entry_swapgs: + SWAPGS + FENCE_SWAPGS_KERNEL_ENTRY + /* EBX = 0 -> SWAPGS required on exit */ + xorl %ebx, %ebx ret SYM_CODE_END(paranoid_entry) -- 2.20.1