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From: Andy Lutomirski <luto@amacapital.net>
To: Sasha Levin <sasha.levin@oracle.com>
Cc: "Andy Lutomirski" <luto@kernel.org>, "X86 ML" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Rik van Riel" <riel@redhat.com>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Denys Vlasenko" <vda.linux@googlemail.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Kees Cook" <keescook@chromium.org>,
	"Brian Gerst" <brgerst@gmail.com>,
	"Paul McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v5 08/17] x86/entry: Add enter_from_user_mode and use it in syscalls
Date: Mon, 21 Dec 2015 14:44:37 -0800
Message-ID: <CALCETrVeckkmEJy+O43cinWriiwUxBSgmjDiSYtLtXhaN9Ud8Q@mail.gmail.com> (raw)
In-Reply-To: <56786606.6090506@oracle.com>

On Mon, Dec 21, 2015 at 12:50 PM, Sasha Levin <sasha.levin@oracle.com> wrote:
> 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:

Weird.  I wonder if you might have hit this while switching context
tracking on a runtime.  (Can you even do that?)

--Andy


>
> [ 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



-- 
Andy Lutomirski
AMA Capital Management, LLC

  reply index

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-03 19:44 [PATCH v5 00/17] x86: Rewrite exit-to-userspace code Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 01/17] selftests/x86: Add a test for 32-bit fast syscall arg faults Andy Lutomirski
2015-07-07 10:49   ` [tip:x86/asm] x86/entry, " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 02/17] x86/entry/64/compat: Fix bad fast syscall arg failure path Andy Lutomirski
2015-07-07 10:49   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 03/17] uml: Fix do_signal() prototype Andy Lutomirski
2015-07-07 10:49   ` [tip:x86/asm] um: " tip-bot for Ingo Molnar
2015-07-03 19:44 ` [PATCH v5 04/17] context_tracking: Add ct_state and CT_WARN_ON Andy Lutomirski
2015-07-07 10:50   ` [tip:x86/asm] context_tracking: Add ct_state() and CT_WARN_ON() tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 05/17] notifiers: Assert that RCU is watching in notify_die Andy Lutomirski
2015-07-07 10:50   ` [tip:x86/asm] notifiers, RCU: Assert that RCU is watching in notify_die() tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 06/17] x86: Move C entry and exit code to arch/x86/entry/common.c Andy Lutomirski
2015-07-07 10:50   ` [tip:x86/asm] x86/entry: Move C entry and exit code to arch/x86/ entry/common.c tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 07/17] x86/traps: Assert that we're in CONTEXT_KERNEL in exception entries Andy Lutomirski
2015-07-07 10:51   ` [tip:x86/asm] x86/traps, context_tracking: Assert that we' re " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 08/17] x86/entry: Add enter_from_user_mode and use it in syscalls Andy Lutomirski
2015-07-07 10:51   ` [tip:x86/asm] x86/entry: Add enter_from_user_mode() " tip-bot for Andy Lutomirski
2015-07-14 23:00     ` Frederic Weisbecker
2015-07-14 23:04       ` Andy Lutomirski
2015-07-14 23:28         ` Frederic Weisbecker
2015-12-21 20:50   ` [PATCH v5 08/17] x86/entry: Add enter_from_user_mode " Sasha Levin
2015-12-21 22:44     ` Andy Lutomirski [this message]
2015-07-03 19:44 ` [PATCH v5 09/17] x86/entry: Add new, comprehensible entry and exit hooks Andy Lutomirski
2015-07-07 10:51   ` [tip:x86/asm] x86/entry: Add new, comprehensible entry and exit handlers written in C tip-bot for Andy Lutomirski
2015-07-14 23:07     ` Frederic Weisbecker
2015-07-15 19:56       ` Linus Torvalds
2015-07-15 20:46         ` Andy Lutomirski
2015-07-15 21:25           ` [PATCH] x86/entry: Fix _TIF_USER_RETURN_NOTIFY check in prepare_exit_to_usermode Andy Lutomirski
2015-07-18  3:25             ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 10/17] x86/entry/64: Really create an error-entry-from-usermode code path Andy Lutomirski
2015-07-07 10:52   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 11/17] x86/entry/64: Migrate 64-bit and compat syscalls to new exit hooks Andy Lutomirski
2015-07-07 10:52   ` [tip:x86/asm] x86/entry/64: Migrate 64-bit and compat syscalls to the new exit handlers and remove old assembly code tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 12/17] x86/asm/entry/64: Save all regs on interrupt entry Andy Lutomirski
2015-07-07 10:52   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 13/17] x86/asm/entry/64: Simplify irq stack pt_regs handling Andy Lutomirski
2015-07-07 10:53   ` [tip:x86/asm] x86/asm/entry/64: Simplify IRQ " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 14/17] x86/asm/entry/64: Migrate error and interrupt exit work to C Andy Lutomirski
2015-07-07 10:53   ` [tip:x86/asm] x86/asm/entry/64: Migrate error and IRQ exit work to C and remove old assembly code tip-bot for Andy Lutomirski
2015-08-11 22:18     ` Frederic Weisbecker
2015-08-11 22:25       ` Andy Lutomirski
2015-08-11 22:49         ` Frederic Weisbecker
2015-08-11 22:59           ` Andy Lutomirski
2015-08-12  1:02             ` Paul E. McKenney
2015-08-12 13:13             ` Frederic Weisbecker
2015-08-11 22:38     ` Frederic Weisbecker
2015-08-11 22:51       ` Andy Lutomirski
2015-08-11 23:22         ` Frederic Weisbecker
2015-08-11 23:33           ` Andy Lutomirski
2015-08-12 13:32             ` Frederic Weisbecker
2015-08-12 14:59               ` Andy Lutomirski
2015-08-18 22:34                 ` Frederic Weisbecker
2015-08-18 22:40                   ` Andy Lutomirski
2015-08-19 17:18                     ` Frederic Weisbecker
2015-08-19 18:02                       ` Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 15/17] x86/entry: Remove exception_enter from most trap handlers Andy Lutomirski
2015-07-07 10:53   ` [tip:x86/asm] x86/entry: Remove exception_enter() " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 16/17] x86/entry: Remove SCHEDULE_USER and asm/context-tracking.h Andy Lutomirski
2015-07-07 10:54   ` [tip:x86/asm] x86/entry: Remove SCHEDULE_USER and asm/ context-tracking.h tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 17/17] x86/irq: Document how IRQ context tracking works and add an assertion Andy Lutomirski
2015-07-07 10:54   ` [tip:x86/asm] x86/irq, context_tracking: Document how IRQ context tracking works and add an RCU assertion tip-bot for Andy Lutomirski
2015-07-14 23:26     ` Frederic Weisbecker
2015-07-14 23:33       ` Andy Lutomirski
2015-07-18 13:23         ` Frederic Weisbecker
2015-07-18 14:10           ` Paul E. McKenney
2015-07-07 11:12 ` [PATCH v5 00/17] x86: Rewrite exit-to-userspace code Ingo Molnar
2015-07-07 16:03   ` Andy Lutomirski
2015-07-07 17:55     ` [PATCH] x86/entry/64: Fix warning on compat syscalls with CONFIG_AUDITSYSCALL=n Andy Lutomirski
2015-07-08  9:57       ` [tip:x86/asm] x86/entry/64: Fix IRQ state confusion and related warning on compat syscalls with CONFIG_AUDITSYSCALL =n tip-bot for Andy Lutomirski
2015-07-08 19:12       ` tip-bot for Andy Lutomirski

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