From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751784AbcFXPfT (ORCPT ); Fri, 24 Jun 2016 11:35:19 -0400 Received: from mail-oi0-f65.google.com ([209.85.218.65]:34166 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751555AbcFXPfO (ORCPT ); Fri, 24 Jun 2016 11:35:14 -0400 MIME-Version: 1.0 In-Reply-To: <20160624153001.b5urlxdpvliqqqji@treble> References: <2bae70091dd75abc881259747987979156f2f789.1466741835.git.luto@kernel.org> <20160624153001.b5urlxdpvliqqqji@treble> From: Brian Gerst Date: Fri, 24 Jun 2016 11:35:13 -0400 Message-ID: Subject: Re: [PATCH v4 11/16] x86/dumpstack: When OOPSing, rewind the stack before do_exit To: Josh Poimboeuf Cc: Andy Lutomirski , "the arch/x86 maintainers" , Linux Kernel Mailing List , linux-arch@vger.kernel.org, Borislav Petkov , Nadav Amit , Kees Cook , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Jann Horn , Heiko Carstens Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 24, 2016 at 11:30 AM, Josh Poimboeuf wrote: > On Thu, Jun 23, 2016 at 09:23:06PM -0700, Andy Lutomirski wrote: >> If we call do_exit with a clean stack, we greatly reduce the risk of >> recursive oopses due to stack overflow in do_exit, and we allow >> do_exit to work even if we OOPS from an IST stack. The latter gives >> us a much better chance of surviving long enough after we detect a >> stack overflow to write out our logs. >> >> I intentionally separated this from the preceding patch that >> disables do_exit-on-OOPS on IST stacks. This way, if we need to >> revert this patch, we still end up in an acceptable state wrt stack >> overflow handling. >> >> Signed-off-by: Andy Lutomirski >> --- >> arch/x86/entry/entry_32.S | 11 +++++++++++ >> arch/x86/entry/entry_64.S | 11 +++++++++++ >> arch/x86/kernel/dumpstack.c | 13 +++++++++---- >> 3 files changed, 31 insertions(+), 4 deletions(-) >> >> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S >> index 983e5d3a0d27..0b56666e6039 100644 >> --- a/arch/x86/entry/entry_32.S >> +++ b/arch/x86/entry/entry_32.S >> @@ -1153,3 +1153,14 @@ ENTRY(async_page_fault) >> jmp error_code >> END(async_page_fault) >> #endif >> + >> +ENTRY(rewind_stack_do_exit) >> + /* Prevent any naive code from trying to unwind to our caller. */ >> + xorl %ebp, %ebp >> + >> + movl PER_CPU_VAR(cpu_current_top_of_stack), %esi >> + leal -TOP_OF_KERNEL_STACK_PADDING-PTREGS_SIZE(%esi), %esp >> + >> + call do_exit >> +1: jmp 1b >> +END(rewind_stack_do_exit) >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >> index 9ee0da1807ed..b846875aeea6 100644 >> --- a/arch/x86/entry/entry_64.S >> +++ b/arch/x86/entry/entry_64.S >> @@ -1423,3 +1423,14 @@ ENTRY(ignore_sysret) >> mov $-ENOSYS, %eax >> sysret >> END(ignore_sysret) >> + >> +ENTRY(rewind_stack_do_exit) >> + /* Prevent any naive code from trying to unwind to our caller. */ >> + xorl %ebp, %ebp > > s/ebp/rbp/g/ ? No, this quirk of the x86-64 instruction set will zero-extend to 64-bits without needing a REX prefix. -- Brian Gerst