From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f70.google.com (mail-pl0-f70.google.com [209.85.160.70]) by kanga.kvack.org (Postfix) with ESMTP id DF1986B027B for ; Wed, 22 Nov 2017 19:36:06 -0500 (EST) Received: by mail-pl0-f70.google.com with SMTP id 62so37518plc.6 for ; Wed, 22 Nov 2017 16:36:06 -0800 (PST) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTPS id b6si1365002pgt.534.2017.11.22.16.36.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 Nov 2017 16:36:05 -0800 (PST) Subject: [PATCH 11/23] x86, kaiser: map entry stack variables From: Dave Hansen Date: Wed, 22 Nov 2017 16:34:59 -0800 References: <20171123003438.48A0EEDE@viggo.jf.intel.com> In-Reply-To: <20171123003438.48A0EEDE@viggo.jf.intel.com> Message-Id: <20171123003459.C0FF167A@viggo.jf.intel.com> Sender: owner-linux-mm@kvack.org List-ID: 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 There are times where the kernel is entered but there is not a safe stack, like at SYSCALL entry. To obtain a safe stack, the per-cpu variables 'rsp_scratch' and 'cpu_current_top_of_stack' are used to save the old %rsp value and to find where the kernel stack should start. You can not directly manipulate the CR3 register. You can only 'MOV' to it from another register, which means a register must be clobbered in order to do any CR3 manipulation. User-mapping these variables allows us to obtain a safe stack and use it for temporary storage *before* CR3 is switched. 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 2017-11-22 15:45:50.128619736 -0800 +++ b/arch/x86/kernel/cpu/common.c 2017-11-22 15:45:50.134619736 -0800 @@ -1524,7 +1524,7 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count); * the top of the kernel 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 2017-11-22 15:45:50.130619736 -0800 +++ b/arch/x86/kernel/process_64.c 2017-11-22 15:45:50.134619736 -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) _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org