From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1947871AbcHRNSC (ORCPT ); Thu, 18 Aug 2016 09:18:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42660 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946001AbcHRNSA (ORCPT ); Thu, 18 Aug 2016 09:18:00 -0400 From: Josh Poimboeuf To: Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Linus Torvalds , Steven Rostedt , Brian Gerst , Kees Cook , Peter Zijlstra , Frederic Weisbecker , Byungchul Park , Nilay Vaish Subject: [PATCH v4 14/57] x86/head: put real return address on idle task stack Date: Thu, 18 Aug 2016 08:05:54 -0500 Message-Id: In-Reply-To: References: X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 18 Aug 2016 13:07:04 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The frame at the end of each idle task stack has a zeroed return address. This is inconsistent with real task stacks, which have a real return address at that spot. This inconsistency can be confusing for stack unwinders. It also hides useful information about what asm code was involved in calling into C. Make it a real address by using the side effect of a call instruction to push the instruction pointer on the stack. Reviewed-by: Andy Lutomirski Signed-off-by: Josh Poimboeuf --- arch/x86/kernel/head_64.S | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 3621ad2..c90f481 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -298,8 +298,9 @@ ENTRY(start_cpu) * REX.W + FF /5 JMP m16:64 Jump far, absolute indirect, * address given in m16:64. */ - movq initial_code(%rip),%rax - pushq $0 # fake return address to stop unwinder + call 1f # put return address on stack for unwinder +1: xorq %rbp, %rbp # clear frame pointer + movq initial_code(%rip), %rax pushq $__KERNEL_CS # set correct cs pushq %rax # target address in negative space lretq -- 2.7.4