From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 8573C6B0005 for ; Thu, 1 Mar 2018 08:34:33 -0500 (EST) Received: by mail-wr0-f198.google.com with SMTP id j4so4045056wrg.11 for ; Thu, 01 Mar 2018 05:34:33 -0800 (PST) Received: from theia.8bytes.org (8bytes.org. [2a01:238:4383:600:38bc:a715:4b6d:a889]) by mx.google.com with ESMTPS id v28si3538603edd.488.2018.03.01.05.34.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Mar 2018 05:34:32 -0800 (PST) Date: Thu, 1 Mar 2018 14:34:30 +0100 From: Joerg Roedel Subject: Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI entry/exit points Message-ID: <20180301133430.wda4qesqhxnww7d6@8bytes.org> References: <1518168340-9392-1-git-send-email-joro@8bytes.org> <1518168340-9392-13-git-send-email-joro@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Waiman Long Cc: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Andy Lutomirski , Dave Hansen , Josh Poimboeuf , Juergen Gross , Peter Zijlstra , Borislav Petkov , Jiri Kosina , Boris Ostrovsky , Brian Gerst , David Laight , Denys Vlasenko , Eduardo Valentin , Greg KH , Will Deacon , aliguori@amazon.com, daniel.gruss@iaik.tugraz.at, hughd@google.com, keescook@google.com, Andrea Arcangeli , Waiman Long , Pavel Machek , jroedel@suse.de On Tue, Feb 27, 2018 at 02:18:36PM -0500, Waiman Long wrote: > > + /* Make sure we are running on kernel cr3 */ > > + SWITCH_TO_KERNEL_CR3 scratch_reg=%eax > > + > > xorl %edx, %edx # error code 0 > > movl %esp, %eax # pt_regs pointer > > > > The debug exception calls ret_from_exception on exit. If coming from > userspace, the C function prepare_exit_to_usermode() will be called. > With the PTI-32 code, it means that function will be called with the > entry stack instead of the task stack. This can be problematic as macro > like current won't work anymore. Okay, I had another look at the debug handler. As I said before, it already handles the from-entry-stack case, but with these patches it gets more likely that we actually hit that path. Also, with the special handling for from-kernel-with-entry-stack situations we can simplify the debug handler and make it more robust with the diff below. Thoughts? diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 8c149f5..844aff1 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -1318,33 +1318,14 @@ ENTRY(debug) ASM_CLAC pushl $-1 # mark this as an int - SAVE_ALL + SAVE_ALL switch_stacks=1 ENCODE_FRAME_POINTER - /* Make sure we are running on kernel cr3 */ - SWITCH_TO_KERNEL_CR3 scratch_reg=%eax - xorl %edx, %edx # error code 0 movl %esp, %eax # pt_regs pointer - /* Are we currently on the SYSENTER stack? */ - movl PER_CPU_VAR(cpu_entry_area), %ecx - addl $CPU_ENTRY_AREA_entry_stack + SIZEOF_entry_stack, %ecx - subl %eax, %ecx /* ecx = (end of entry_stack) - esp */ - cmpl $SIZEOF_entry_stack, %ecx - jb .Ldebug_from_sysenter_stack - - TRACE_IRQS_OFF - call do_debug - jmp ret_from_exception - -.Ldebug_from_sysenter_stack: - /* We're on the SYSENTER stack. Switch off. */ - movl %esp, %ebx - movl PER_CPU_VAR(cpu_current_top_of_stack), %esp TRACE_IRQS_OFF call do_debug - movl %ebx, %esp jmp ret_from_exception END(debug) -- 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