From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751451AbbLUUuu (ORCPT ); Mon, 21 Dec 2015 15:50:50 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:25347 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751195AbbLUUus (ORCPT ); Mon, 21 Dec 2015 15:50:48 -0500 Subject: Re: [PATCH v5 08/17] x86/entry: Add enter_from_user_mode and use it in syscalls To: Andy Lutomirski , x86@kernel.org, linux-kernel@vger.kernel.org References: <853b42420066ec3fb856779cdc223a6dcb5d355b.1435952415.git.luto@kernel.org> Cc: =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= , Rik van Riel , Oleg Nesterov , Denys Vlasenko , Borislav Petkov , Kees Cook , Brian Gerst , paulmck@linux.vnet.ibm.com From: Sasha Levin Message-ID: <56786606.6090506@oracle.com> Date: Mon, 21 Dec 2015 15:50:14 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 MIME-Version: 1.0 In-Reply-To: <853b42420066ec3fb856779cdc223a6dcb5d355b.1435952415.git.luto@kernel.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/03/2015 03:44 PM, Andy Lutomirski wrote: > Changing the x86 context tracking hooks is dangerous because there > are no good checks that we track our context correctly. Add a > helper to check that we're actually in CONTEXT_USER when we enter > from user mode and wire it up for syscall entries. > > Subsequent patches will wire this up for all non-NMI entries as > well. NMIs are their own special beast and cannot currently switch > overall context tracking state. Instead, they have their own > special RCU hooks. > > This is a tiny speedup if !CONFIG_CONTEXT_TRACKING (removes a > branch) and a tiny slowdown if CONFIG_CONTEXT_TRACING (adds a layer > of indirection). Eventually, we should fix up the core context > tracking code to supply a function that does what we want (and can > be much simpler than user_exit), which will enable us to get rid of > the extra call. Hey Andy, I see the following warning in today's -next: [ 2162.706868] ------------[ cut here ]------------ [ 2162.708021] WARNING: CPU: 4 PID: 28801 at arch/x86/entry/common.c:44 enter_from_user_mode+0x1c/0x50() [ 2162.709466] Modules linked in: [ 2162.709998] CPU: 4 PID: 28801 Comm: trinity-c375 Tainted: G B 4.4.0-rc5-next-20151221-sasha-00020-g840272e-dirty #2753 [ 2162.711847] 0000000000000000 00000000f17e6fcd ffff880292d5fe08 ffffffffa4045334 [ 2162.713108] 0000000041b58ab3 ffffffffaf66686b ffffffffa4045289 ffff880292d5fdc0 [ 2162.714544] 0000000000000000 00000000f17e6fcd ffffffffa23cf466 0000000000000004 [ 2162.715793] Call Trace: [ 2162.716229] dump_stack (lib/dump_stack.c:52) [ 2162.719021] warn_slowpath_common (kernel/panic.c:484) [ 2162.721014] warn_slowpath_null (kernel/panic.c:518) [ 2162.721950] enter_from_user_mode (arch/x86/entry/common.c:44 (discriminator 7) include/linux/context_tracking_state.h:30 (discriminator 7) include/linux/context_tracking.h:30 (discriminator 7) arch/x86/entry/common.c:45 (discriminator 7)) [ 2162.722911] syscall_trace_enter_phase1 (arch/x86/entry/common.c:94) [ 2162.726914] tracesys (arch/x86/entry/entry_64.S:241) [ 2162.727704] ---[ end trace 1e5b49c361cbfe8b ]--- [ 2162.728468] BUG: scheduling while atomic: trinity-c375/28801/0x00000401 [ 2162.729517] Modules linked in: [ 2162.730020] Preemption disabled param_attr_store (kernel/params.c:625) [ 2162.731304] [ 2162.731579] CPU: 4 PID: 28801 Comm: trinity-c375 Tainted: G B W 4.4.0-rc5-next-20151221-sasha-00020-g840272e-dirty #2753 [ 2162.733432] 0000000000000000 00000000f17e6fcd ffff880292d5fe20 ffffffffa4045334 [ 2162.734778] 0000000041b58ab3 ffffffffaf66686b ffffffffa4045289 ffff880292d5fde0 [ 2162.736036] fffffffface198f9 00000000f17e6fcd ffff880292d5fe50 0000000000000282 [ 2162.737309] Call Trace: [ 2162.737718] dump_stack (lib/dump_stack.c:52) [ 2162.740566] __schedule_bug (kernel/sched/core.c:3102) [ 2162.741498] __schedule (./arch/x86/include/asm/preempt.h:27 kernel/sched/core.c:3116 kernel/sched/core.c:3225) [ 2162.742391] schedule (kernel/sched/core.c:3312 (discriminator 1)) [ 2162.743221] exit_to_usermode_loop (arch/x86/entry/common.c:246) [ 2162.744331] syscall_return_slowpath (arch/x86/entry/common.c:282 include/linux/context_tracking_state.h:30 include/linux/context_tracking.h:24 arch/x86/entry/common.c:284 arch/x86/entry/common.c:344) [ 2162.745364] int_ret_from_sys_call (arch/x86/entry/entry_64.S:282) Thanks, Sasha