From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932428AbbBZO0n (ORCPT ); Thu, 26 Feb 2015 09:26:43 -0500 Received: from smtp3-g21.free.fr ([212.27.42.3]:53233 "EHLO smtp3-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932146AbbBZO0l (ORCPT ); Thu, 26 Feb 2015 09:26:41 -0500 Date: Thu, 26 Feb 2015 15:26:21 +0100 From: Sabrina Dubroca To: Denys Vlasenko Cc: Andy Lutomirski , Denys Vlasenko , Andrey Wagin , Ingo Molnar , Linus Torvalds , Oleg Nesterov , Borislav Petkov , "H. Peter Anvin" , Frederic Weisbecker , X86 ML , Alexei Starovoitov , Will Drewry , Kees Cook , LKML Subject: Re: [PATCH 2/3 v3] x86: entry_64.S: always allocate complete "struct pt_regs" Message-ID: <20150226142621.GA10708@kria> References: <1423778052-21038-2-git-send-email-dvlasenk@redhat.com> <54EE1799.2000602@redhat.com> <54EE3E94.7060208@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2015-02-26, 14:54:33 +0100, Denys Vlasenko wrote: > On Thu, Feb 26, 2015 at 1:11 PM, Denys Vlasenko > wrote: > > On Thu, Feb 26, 2015 at 10:55 AM, Denys Vlasenko > > wrote: > >> On Wed, Feb 25, 2015 at 10:59 PM, Andy Lutomirski wrote: > >> In addition to my previous tests, I ran my home machine with > >> patched kernel. Unfortunately, it works for me :( > >> > >> Will try on yet another machine. > > > > And voila, it does happen on another machine :) > > > > I'm debugging it right now. Looks like 64-bit syscalls just stop working > > at some point in new processes. That is, existing process is alive and well, > > but children get SEGV after fork (most likely on any syscall64 they do, > > not after fork per se. They eventually manage to kill themselves - > > not trivial when exit syscall isn't working either - by tripping on HLT insn). > > > > 32-bit syscalls (int 80) continue to work. Fork, exec, whatever you want. > > I have static 32-bit busybox binary and everything works there. > > > > Also, any 64-bit process which was under strace continues to work correctly, > > including forks and execs. > > > > This points towards some bug on fast path sysret64 code. Looking for it. > > audit=0 makes crashes disappear. Ah, yes. > I found the problem. If syscall_trace_enter_phase1 returns 0, > I restore %rax from pt_regs->ax, but should restore it from > pt_regs->orig_ax: > > call syscall_trace_enter_phase1 > test %rax, %rax > jnz tracesys_phase2 /* if needed, run the slow path */ > - RESTORE_C_REGS /* else restore clobbered regs */ > + RESTORE_C_REGS_EXCEPT_RAX /* else restore clobbered regs */ > + movq ORIG_RAX-ARGOFFSET(%rsp),%rax > jmp system_call_fastpath /* and return to the fast path */ with s/-ARGOFFSET// on top of next-20150224, that works. Thanks, Denys. -- Sabrina