From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759217AbcLSKz4 (ORCPT ); Mon, 19 Dec 2016 05:55:56 -0500 Received: from terminus.zytor.com ([198.137.202.10]:58108 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758306AbcLSKzc (ORCPT ); Mon, 19 Dec 2016 05:55:32 -0500 Date: Mon, 19 Dec 2016 02:54:57 -0800 From: tip-bot for Josh Poimboeuf Message-ID: Cc: tglx@linutronix.de, luto@amacapital.net, jpoimboe@redhat.com, bp@alien8.de, hpa@zytor.com, mingo@kernel.org, linux-kernel@vger.kernel.org Reply-To: jpoimboe@redhat.com, luto@amacapital.net, tglx@linutronix.de, bp@alien8.de, hpa@zytor.com, mingo@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <9d7b4eb8cf55a7d6002cb738f25c23e7429c99a0.1481904011.git.jpoimboe@redhat.com> References: <9d7b4eb8cf55a7d6002cb738f25c23e7429c99a0.1481904011.git.jpoimboe@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/unwind: Adjust last frame check for aligned function stacks Git-Commit-ID: 8023e0e2a48d45e8d5363081fad9f7ed4402f953 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 8023e0e2a48d45e8d5363081fad9f7ed4402f953 Gitweb: http://git.kernel.org/tip/8023e0e2a48d45e8d5363081fad9f7ed4402f953 Author: Josh Poimboeuf AuthorDate: Fri, 16 Dec 2016 10:05:05 -0600 Committer: Thomas Gleixner CommitDate: Mon, 19 Dec 2016 11:47:05 +0100 x86/unwind: Adjust last frame check for aligned function stacks Somehow, CONFIG_PARAVIRT=n convinces gcc to change the x86_64_start_kernel() prologue from: 0000000000000129 : 129: 55 push %rbp 12a: 48 89 e5 mov %rsp,%rbp to: 0000000000000124 : 124: 4c 8d 54 24 08 lea 0x8(%rsp),%r10 129: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp 12d: 41 ff 72 f8 pushq -0x8(%r10) 131: 55 push %rbp 132: 48 89 e5 mov %rsp,%rbp This is an unusual pattern which aligns rsp (though in this case it's already aligned) and saves the start_cpu() return address again on the stack before storing the frame pointer. The unwinder assumes the last stack frame header is at a certain offset, but the above code breaks that assumption, resulting in the following warning: WARNING: kernel stack frame pointer at ffffffff82e03f40 in swapper:0 has bad value (null) Fix it by checking for the last task stack frame at the aligned offset in addition to the normal unaligned offset. Fixes: acb4608ad186 ("x86/unwind: Create stack frames for saved syscall registers") Reported-by: Borislav Petkov Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Link: http://lkml.kernel.org/r/9d7b4eb8cf55a7d6002cb738f25c23e7429c99a0.1481904011.git.jpoimboe@redhat.com Signed-off-by: Thomas Gleixner --- arch/x86/kernel/unwind_frame.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c index ea7b7f9..33aeaae 100644 --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -46,7 +46,14 @@ static bool is_last_task_frame(struct unwind_state *state) unsigned long bp = (unsigned long)state->bp; unsigned long regs = (unsigned long)task_pt_regs(state->task); - return bp == regs - FRAME_HEADER_SIZE; + /* + * We have to check for the last task frame at two different locations + * because gcc can occasionally decide to realign the stack pointer and + * change the offset of the stack frame by a word in the prologue of a + * function called by head/entry code. + */ + return bp == regs - FRAME_HEADER_SIZE || + bp == regs - FRAME_HEADER_SIZE - sizeof(long); } /*