From: Masami Hiramatsu <mhiramat@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Steven Rostedt <rostedt@goodmis.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
stable <stable@vger.kernel.org>,
Changbin Du <changbin.du@gmail.com>, Jann Horn <jannh@google.com>,
Kees Cook <keescook@chromium.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault
Date: Mon, 25 Feb 2019 17:09:45 +0900 [thread overview]
Message-ID: <20190225170945.d808659362b364298c3206e9@kernel.org> (raw)
In-Reply-To: <CALCETrUHASYthoWGB-CLcvtNEhAp83aA4+iGHtqjtX4ML6chfA@mail.gmail.com>
On Sun, 24 Feb 2019 20:49:45 -0800
Andy Lutomirski <luto@kernel.org> wrote:
> On Sun, Feb 24, 2019 at 6:40 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> >
> > On Sun, 24 Feb 2019 09:26:45 -0800
> > Linus Torvalds <torvalds@linux-foundation.org> wrote:
> >
> > > On Sun, Feb 24, 2019 at 7:18 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > > >
> > > > On Sat, 23 Feb 2019 20:38:03 -0800
> > > > Andy Lutomirski <luto@kernel.org> wrote:
> > > > >
> > > > > Can we just get rid of this might_sleep()? access_ok() doesn't sleep
> > > > > as far as I know.
> > > >
> > > > Hmm, which might_sleep() would you pointed? What I talked was a
> > > > WARN_ON_ONCE(!in_task()) in access_ok() on x86 (only!), and in_task() just
> > > > checks preempt_count.
> > >
> > > So the in_task() check does kind of make sense. Using "access_ok()"
> > > outside of task context is certainly an odd thing, for several
> > > reasons. The main one being simply that outside of task context, the
> > > whole "which task" question is open, and you don't know if the task is
> > > the active one, and so it's not clear if whatever task you interrupt
> > > might have done "set_fs()" or not.
> >
> > Ah I got it. Usual case access_ok() in IRQ handler is strange.
> >
> > >
> > > So PeterZ isn't wrong:
> > >
> > > > I guess PeterZ assumed that access_ok() is used only with user space access
> > > > APIs (e.g. copy_from_user) which can cause page-fault and locks mm (and might
> > > > sleep :)), but now we are trying to use access_ok() with new functions which
> > > > disables page-fault and just return -EFAULT.
> > >
> > > .. but in this case, if we do it all *within* code that saves and
> > > restores the user access flag with get_fs/set_fs, access_ok() would be
> > > ok and it doesn't have the above issue.
> > >
> > > So access_ok() in _general_ is absolutely not safe to do from
> > > interrupts, but within the context of probing user memory from a
> > > tracing event it just happens to be ok.
> >
> > Hmm, but user can specify user-memory access from the tracing event
> > which is located in interrupt handler. So I understand that it is safe
> > only if we correctly setup access flag with get_fs/set_fs, is that
> > correct?
> >
> > > It would be lovely to have a special macro for this, and keep the
> > > warning for the general case, but because this is a "every
> > > architecture needs to build their own" it's probably too painful.
> >
> > Agreed.
>
> This should probably go with whatever effort makes nmi_uaccess_ok()
> available on all architectures. That being said, how about just
> making copy_from_user_nmi() work on all architectures, even if it just
> fails unconditionally on some of them?
I think even if we have copy_from_user_nmi(), we need something like
nmi_uaccess_ok() because without it we can not correctly use
__copy_from_user_inatomic()...
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2019-02-25 8:09 UTC|newest]
Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-15 17:47 [PATCH 0/2 v2] [GIT PULL (take two)] tracing: Two more fixes Steven Rostedt
2019-02-15 17:47 ` [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault Steven Rostedt
2019-02-15 17:55 ` Linus Torvalds
2019-02-15 22:15 ` Steven Rostedt
2019-02-15 23:49 ` Andy Lutomirski
2019-02-16 0:19 ` Steven Rostedt
2019-02-16 1:32 ` Andy Lutomirski
2019-02-16 2:08 ` Steven Rostedt
2019-02-16 2:14 ` Andy Lutomirski
2019-02-16 2:21 ` Steven Rostedt
2019-02-18 17:58 ` Linus Torvalds
2019-02-18 18:23 ` Linus Torvalds
2019-02-19 16:18 ` Steven Rostedt
2019-02-19 18:43 ` Linus Torvalds
2019-02-19 19:03 ` Steven Rostedt
2019-02-20 8:10 ` Masami Hiramatsu
2019-02-20 13:57 ` Jann Horn
2019-02-20 14:47 ` Steven Rostedt
2019-02-20 15:08 ` Masami Hiramatsu
2019-02-20 14:49 ` Steven Rostedt
2019-02-20 16:04 ` Masami Hiramatsu
2019-02-20 16:42 ` Steven Rostedt
2019-02-21 7:37 ` Masami Hiramatsu
2019-02-22 8:27 ` Masami Hiramatsu
2019-02-22 8:35 ` Masami Hiramatsu
2019-02-22 17:43 ` Linus Torvalds
2019-02-22 17:48 ` Andy Lutomirski
2019-02-22 18:28 ` Linus Torvalds
2019-02-22 19:52 ` Andy Lutomirski
2019-02-22 19:27 ` Alexei Starovoitov
2019-02-22 19:30 ` Steven Rostedt
2019-02-22 19:34 ` Alexei Starovoitov
2019-02-22 19:39 ` Steven Rostedt
2019-02-22 19:55 ` Andy Lutomirski
2019-02-22 21:43 ` Jann Horn
2019-02-22 22:08 ` Nadav Amit
2019-02-22 22:17 ` Jann Horn
2019-02-22 22:21 ` Nadav Amit
2019-02-22 22:39 ` Nadav Amit
2019-02-22 23:02 ` Jann Horn
2019-02-22 23:22 ` Nadav Amit
2019-02-22 23:59 ` Andy Lutomirski
2019-02-23 0:03 ` Alexei Starovoitov
2019-02-23 0:15 ` Nadav Amit
2019-02-24 19:35 ` Andy Lutomirski
2019-02-25 13:36 ` Masami Hiramatsu
2019-02-22 21:20 ` Linus Torvalds
2019-02-22 21:38 ` David Miller
2019-02-22 21:59 ` Linus Torvalds
2019-02-22 22:51 ` Alexei Starovoitov
2019-02-22 23:11 ` Jann Horn
2019-02-22 23:16 ` David Miller
2019-02-22 23:16 ` Linus Torvalds
2019-02-22 23:56 ` Alexei Starovoitov
2019-02-23 0:08 ` Linus Torvalds
2019-02-23 2:28 ` Alexei Starovoitov
2019-02-23 2:32 ` Linus Torvalds
2019-02-23 3:02 ` Steven Rostedt
2019-02-23 4:51 ` Masami Hiramatsu
2019-02-26 3:57 ` Christoph Hellwig
2019-02-26 15:24 ` Joel Fernandes
2019-02-28 12:29 ` Masami Hiramatsu
2019-02-28 15:18 ` Joel Fernandes
2019-02-23 3:47 ` Masami Hiramatsu
2019-02-24 0:44 ` Steven Rostedt
2019-02-24 4:38 ` Andy Lutomirski
2019-02-24 15:17 ` Masami Hiramatsu
2019-02-24 17:26 ` Linus Torvalds
2019-02-25 2:40 ` Masami Hiramatsu
2019-02-25 4:49 ` Andy Lutomirski
2019-02-25 8:09 ` Masami Hiramatsu [this message]
2019-02-25 16:40 ` Steven Rostedt
2019-02-26 1:35 ` Masami Hiramatsu
2019-02-25 8:33 ` Peter Zijlstra
2019-02-25 14:52 ` Peter Zijlstra
2019-02-25 16:48 ` Kees Cook
2019-02-25 16:58 ` Andy Lutomirski
2019-02-25 17:07 ` Kees Cook
2019-02-21 7:52 ` Masami Hiramatsu
2019-02-21 14:36 ` Steven Rostedt
2019-02-21 15:58 ` Masami Hiramatsu
2019-02-21 16:16 ` Masami Hiramatsu
2019-02-21 16:32 ` Steven Rostedt
2019-02-23 14:48 ` Masami Hiramatsu
2019-02-15 17:47 ` [PATCH 2/2 v2] tracing: Fix number of entries in trace header Steven Rostedt
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