From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751680AbcFXPsh (ORCPT ); Fri, 24 Jun 2016 11:48:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35618 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751235AbcFXPsc (ORCPT ); Fri, 24 Jun 2016 11:48:32 -0400 Date: Fri, 24 Jun 2016 10:48:29 -0500 From: Josh Poimboeuf To: Brian Gerst 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 Subject: Re: [PATCH v4 11/16] x86/dumpstack: When OOPSing, rewind the stack before do_exit Message-ID: <20160624154829.mfh7e5it22rssupm@treble> References: <2bae70091dd75abc881259747987979156f2f789.1466741835.git.luto@kernel.org> <20160624153001.b5urlxdpvliqqqji@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Fri, 24 Jun 2016 15:48:32 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 24, 2016 at 11:35:13AM -0400, Brian Gerst wrote: > 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. Ah, so it makes the instruction smaller. And I see that gcc also does the same. In that case: Reviewed-by: Josh Poimboeuf -- Josh