From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752808AbdKHTr3 (ORCPT ); Wed, 8 Nov 2017 14:47:29 -0500 Received: from mga06.intel.com ([134.134.136.31]:12767 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752648AbdKHTr0 (ORCPT ); Wed, 8 Nov 2017 14:47:26 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,365,1505804400"; d="scan'208";a="173893839" Subject: [PATCH 15/30] x86, kaiser: map entry stack variables To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, dave.hansen@linux.intel.com, moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at, richard.fellner@student.tugraz.at, luto@kernel.org, torvalds@linux-foundation.org, keescook@google.com, hughd@google.com, x86@kernel.org From: Dave Hansen Date: Wed, 08 Nov 2017 11:47:15 -0800 References: <20171108194646.907A1942@viggo.jf.intel.com> In-Reply-To: <20171108194646.907A1942@viggo.jf.intel.com> Message-Id: <20171108194715.3292DBFB@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen There are times that we enter the kernel and do not have a safe stack, like at SYSCALL entry. We use the per-cpu vairables 'rsp_scratch' and 'cpu_current_top_of_stack' to save off the old %rsp and find a safe place to have a stack. You can not directly manipulate the CR3 register. You can only 'MOV' to it from another register, which means we need to clobber a register in order to do any CR3 manipulation. User-mapping these variables allows us to obtain a safe stack *before* we switch the CR3 value. Signed-off-by: Dave Hansen Cc: Moritz Lipp Cc: Daniel Gruss Cc: Michael Schwarz Cc: Richard Fellner Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Kees Cook Cc: Hugh Dickins Cc: x86@kernel.org --- b/arch/x86/kernel/cpu/common.c | 2 +- b/arch/x86/kernel/process_64.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff -puN arch/x86/kernel/cpu/common.c~kaiser-user-map-stack-helper-vars arch/x86/kernel/cpu/common.c --- a/arch/x86/kernel/cpu/common.c~kaiser-user-map-stack-helper-vars 2017-11-08 10:45:34.001681383 -0800 +++ b/arch/x86/kernel/cpu/common.c 2017-11-08 10:45:34.007681383 -0800 @@ -1447,7 +1447,7 @@ DEFINE_PER_CPU_ALIGNED(struct stack_cana * trampoline, not the thread stack. Use an extra percpu variable to track * the top of the kernel stack directly. */ -DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) = +DEFINE_PER_CPU_USER_MAPPED(unsigned long, cpu_current_top_of_stack) = (unsigned long)&init_thread_union + THREAD_SIZE; EXPORT_PER_CPU_SYMBOL(cpu_current_top_of_stack); diff -puN arch/x86/kernel/process_64.c~kaiser-user-map-stack-helper-vars arch/x86/kernel/process_64.c --- a/arch/x86/kernel/process_64.c~kaiser-user-map-stack-helper-vars 2017-11-08 10:45:34.003681383 -0800 +++ b/arch/x86/kernel/process_64.c 2017-11-08 10:45:34.007681383 -0800 @@ -59,7 +59,7 @@ #include #endif -__visible DEFINE_PER_CPU(unsigned long, rsp_scratch); +__visible DEFINE_PER_CPU_USER_MAPPED(unsigned long, rsp_scratch); /* Prints also some state that isn't saved in the pt_regs */ void __show_regs(struct pt_regs *regs, int all) _