From: Jann Horn <jannh@google.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andy Lutomirski <luto@amacapital.net>,
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>,
Kees Cook <keescook@chromium.org>,
Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault
Date: Wed, 20 Feb 2019 14:57:31 +0100 [thread overview]
Message-ID: <CAG48ez0e5b0qmW1kMVEYDKvxn=-FkfRw=0KXUm5_R3aAGU-LJA@mail.gmail.com> (raw)
In-Reply-To: <20190220171019.5e81a4946b56982f324f7c45@kernel.org>
On Wed, Feb 20, 2019 at 9:10 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> On Tue, 19 Feb 2019 14:03:30 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > > > Basically, a kprobe is mostly used for debugging what's happening in a
> > > > live kernel, to read any address.
> > >
> > > My point is that "any address" is not sufficient to begin with. You
> > > need "kernel or user".
> > >
> > > Having a flag for what _kind_ of kernel address is ok might then be
> > > required for other cases if they might not be ok with following page
> > > tables to IO space..
> > >
> >
> > Good point. Looks like we should add a new flag for kprobe
> > trace parameters, that tell kprobes if the address is expected to be
> > user or kernel. That would be good regardless of the duplicate
> > meanings, as we could use copy_from_user without touching KERNEL_DS, if
> > the probe argument specifically states "this is user space". For
> > example, when probing do_sys_open, and you want to read what path string
> > was passed into the kernel.
> >
> > Masami, thoughts?
>
> Let me ensure what you want. So you want to access a "string" in user-space,
> not a data structure? In that case, it is very easy to me. It is enough to
> add a "ustring" type to kprobe events. For example, do_sys_opsn's path
> variable is one example. That will be +0(+0(%si)):ustring, and fetcher
> finally copy the string using strncpy_from_user() instead of
> strncpy_from_unsafe(). (*)
[...]
> (*) BTW, there is another concern to use _from_user APIs in kprobe. Are those
> APIs might sleep??
If you want to access userspace without sleeping, and ignore data in
non-present pages, you can do `pagefault_disable(); err =
__copy_from_user_inatomic(...); pagefault_enable();`. (Actually, maybe
the kernel should have a helper for that...)
next prev parent reply other threads:[~2019-02-20 13:58 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 [this message]
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
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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