From: Andy Lutomirski <luto@amacapital.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
Borislav Petkov <bp@alien8.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Brian Gerst <brgerst@gmail.com>, Jann Horn <jann@thejh.net>,
Ingo Molnar <mingo@kernel.org>,
live-patching@vger.kernel.org
Subject: Re: [PATCH 08/12] x86/dumpstack: Pin the target stack in save_stack_trace_tsk()
Date: Fri, 16 Sep 2016 08:12:40 -0700 [thread overview]
Message-ID: <CALCETrWND-1Zq-rrAGb3ja2sDYctvAp7MgeUr7YGf3HjupsycA@mail.gmail.com> (raw)
In-Reply-To: <20160916074730.GJ5012@twins.programming.kicks-ass.net>
On Fri, Sep 16, 2016 at 12:47 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Sep 15, 2016 at 02:19:38PM -0500, Josh Poimboeuf wrote:
>> On Thu, Sep 15, 2016 at 11:41:25AM -0700, Andy Lutomirski wrote:
>> > I also wouldn't mind trying to do something to prevent ever dumping
>> > the stack of an actively running task. It's definitely safe to dump:
>> >
>> > - current
>> >
>> > - any task that's stopped via ptrace, etc
>> >
>> > - any task on the current CPU if running atomically enough that the
>> > task can't migrate (which probably covers the nasty NMI cases, I hope)
>> >
>> > What's *not* safe AFAIK is /proc/PID/stack. I don't know if we can
>> > somehow fix that short of actually sending an interrupt or NMI to
>> > freeze the task if it's running. I'm also not sure it's worth
>> > worrying about it.
>>
>> Yeah, I proposed a fix for /proc/PID/stack a while back:
>>
>> https://lkml.kernel.org/r/cover.1424109806.git.jpoimboe@redhat.com
>>
>> My idea was to use task_rq_lock() to lock the runqueue and then check
>> tsk->on_cpu. I think Peter wasn't too keen on it.
>
> That basically allows a DoS on the scheduler, since a user can run tasks
> on every cpu (through sys_sched_setaffinity()). Then doing while (1) cat
> /proc/$PID/stack would saturate the rq->lock on every CPU.
>
> The more tasks the merrier.
>
>
Is this worse than it would be if this code used preempt_disable()
(which I think it did until very recently)?
--
Andy Lutomirski
AMA Capital Management, LLC
next prev parent reply other threads:[~2016-09-16 15:13 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-13 21:29 [PATCH 00/12] thread_info cleanups and stack caching Andy Lutomirski
2016-09-13 21:29 ` [PATCH 01/12] x86/asm: Move 'status' from struct thread_info to struct thread_struct Andy Lutomirski
2016-09-15 10:41 ` [tip:x86/asm] x86/asm: Move the thread_info::status field to thread_struct tip-bot for Andy Lutomirski
2016-09-13 21:29 ` [PATCH 02/12] x86/entry: Get rid of pt_regs_to_thread_info() Andy Lutomirski
2016-09-15 6:21 ` Ingo Molnar
2016-09-15 10:42 ` [tip:x86/asm] " tip-bot for Linus Torvalds
2016-09-13 21:29 ` [PATCH 03/12] um: Stop conflating task_struct::stack with thread_info Andy Lutomirski
2016-09-15 6:21 ` Ingo Molnar
2016-09-15 10:42 ` [tip:x86/asm] um/Stop " tip-bot for Linus Torvalds
2016-09-13 21:29 ` [PATCH 04/12] sched: Allow putting thread_info into task_struct Andy Lutomirski
2016-09-15 10:43 ` [tip:x86/asm] sched/core: " tip-bot for Andy Lutomirski
2016-09-13 21:29 ` [PATCH 05/12] x86: Move " Andy Lutomirski
2016-09-15 10:43 ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-13 21:29 ` [PATCH 06/12] sched: Add try_get_task_stack() and put_task_stack() Andy Lutomirski
2016-09-13 21:29 ` [PATCH 07/12] kthread: to_live_kthread() needs try_get_task_stack() Andy Lutomirski
2016-09-13 21:29 ` [PATCH 08/12] x86/dumpstack: Pin the target stack in save_stack_trace_tsk() Andy Lutomirski
2016-09-14 14:55 ` Josh Poimboeuf
2016-09-14 18:22 ` Andy Lutomirski
2016-09-14 18:35 ` Josh Poimboeuf
2016-09-15 18:04 ` Andy Lutomirski
2016-09-15 18:37 ` Josh Poimboeuf
2016-09-15 18:41 ` Andy Lutomirski
2016-09-15 19:19 ` Josh Poimboeuf
2016-09-16 7:47 ` Peter Zijlstra
2016-09-16 15:12 ` Andy Lutomirski [this message]
2016-09-16 15:31 ` Peter Zijlstra
2016-09-16 15:32 ` Andy Lutomirski
2016-09-16 16:35 ` Peter Zijlstra
2016-09-15 6:37 ` Ingo Molnar
[not found] ` <CA+55aFxt=HLrELBE=BXUrWdh6LYs4gtu9S=yCruiDffq4HN80w@mail.gmail.com>
2016-09-15 9:27 ` Ingo Molnar
2016-09-13 21:29 ` [PATCH 09/12] x86/process: Pin the target stack in get_wchan() Andy Lutomirski
2016-09-17 2:00 ` Jann Horn
2016-09-22 22:44 ` Andy Lutomirski
2016-09-22 22:50 ` Andy Lutomirski
2016-09-23 7:43 ` Jann Horn
2016-09-23 18:28 ` Kees Cook
2016-09-23 18:34 ` Jann Horn
2016-09-26 5:10 ` Tycho Andersen
2016-09-13 21:29 ` [PATCH 10/12] lib/syscall: Pin the task stack in collect_syscall() Andy Lutomirski
2016-09-13 21:29 ` [PATCH 11/12] sched: Free the stack early if CONFIG_THREAD_INFO_IN_TASK Andy Lutomirski
2016-09-13 21:29 ` [PATCH 12/12] fork: Cache two thread stacks per cpu if CONFIG_VMAP_STACK is set Andy Lutomirski
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