From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753270AbbCJTWU (ORCPT ); Tue, 10 Mar 2015 15:22:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33126 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751330AbbCJTWS (ORCPT ); Tue, 10 Mar 2015 15:22:18 -0400 Message-ID: <54FF4459.3010306@redhat.com> Date: Tue, 10 Mar 2015 20:22:01 +0100 From: Denys Vlasenko User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Andy Lutomirski , x86@kernel.org, linux-kernel@vger.kernel.org CC: Borislav Petkov , Oleg Nesterov Subject: Re: [PATCH 1/3] x86: Create and use a TOP_OF_KERNEL_STACK_PADDING macro References: <02bf2f54b8dcb76a62a142b6dfe07d4ef7fc582e.1426009661.git.luto@amacapital.net> In-Reply-To: <02bf2f54b8dcb76a62a142b6dfe07d4ef7fc582e.1426009661.git.luto@amacapital.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/10/2015 07:05 PM, Andy Lutomirski wrote: > x86_32, unlike x86_64, pads the top of the kernel stack. Document > this padding and give it a name. > > This should make no change whatsoever to the compiled kernel image. > It also doesn't fix any of the current bugs in this area. > > Signed-off-by: Andy Lutomirski > --- > arch/x86/include/asm/processor.h | 3 ++- > arch/x86/include/asm/thread_info.h | 30 ++++++++++++++++++++++++++++++ > 2 files changed, 32 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h > index 48a61c1c626e..88d9aa745898 100644 > --- a/arch/x86/include/asm/processor.h > +++ b/arch/x86/include/asm/processor.h > @@ -849,7 +849,8 @@ extern unsigned long thread_saved_pc(struct task_struct *tsk); > #define task_pt_regs(task) \ > ({ \ > struct pt_regs *__regs__; \ > - __regs__ = (struct pt_regs *)(KSTK_TOP(task_stack_page(task))-8); \ > + __regs__ = (struct pt_regs *)(KSTK_TOP(task_stack_page(task)) - \ > + TOP_OF_KERNEL_STACK_PADDING); \ > __regs__ - 1; \ > }) The "magic 8" also hides here: /* * Push current_thread_info()->sysenter_return to the stack. * A tiny bit of offset fixup is necessary - 4*4 means the 4 words * pushed above; +8 corresponds to copy_thread's esp0 setting. */ pushl_cfi ((TI_sysenter_return)-THREAD_SIZE+8+4*4)(%esp) ^^^ CFI_REL_OFFSET eip, 0 It may make sense to mention TOP_OF_KERNEL_STACK_PADDING here (there are no useful comments in copy_thread() anymore): movl PT_EFLAGS(%esp), %eax # mix EFLAGS, SS and CS # Warning: PT_OLDSS(%esp) contains the wrong/random values if we # are returning to the kernel. # See comments in process.c:copy_thread() for details. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ maybe s/comments in process.c:copy_thread()/TOP_OF_KERNEL_STACK_PADDING/ ? movb PT_OLDSS(%esp), %ah movb PT_CS(%esp), %al andl $(X86_EFLAGS_VM | (SEGMENT_TI_MASK << 8) | SEGMENT_RPL_MASK), %eax cmpl $((SEGMENT_LDT << 8) | USER_RPL), %eax CFI_REMEMBER_STATE