From: Joel Fernandes <joel@joelfernandes.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Steven Rostedt <rostedt@goodmis.org>,
Andy Lutomirski <luto@amacapital.net>,
will.deacon@arm.com,
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>,
Andy Lutomirski <luto@kernel.org>,
daniel@iogearbox.net, netdev@vger.kernel.org,
bpf@vger.kernel.org, yhs@fb.com
Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault
Date: Thu, 28 Feb 2019 10:18:39 -0500 [thread overview]
Message-ID: <20190228151839.GA159251@google.com> (raw)
In-Reply-To: <20190228212913.20079490b3df88d285664a56@kernel.org>
On Thu, Feb 28, 2019 at 09:29:13PM +0900, Masami Hiramatsu wrote:
> On Tue, 26 Feb 2019 10:24:47 -0500
> Joel Fernandes <joel@joelfernandes.org> wrote:
>
> > On Fri, Feb 22, 2019 at 11:27:05AM -0800, Alexei Starovoitov wrote:
> > > On Fri, Feb 22, 2019 at 09:43:14AM -0800, Linus Torvalds wrote:
> > > >
> > > > Then we should still probably fix up "__probe_kernel_read()" to not
> > > > allow user accesses. The easiest way to do that is actually likely to
> > > > use the "unsafe_get_user()" functions *without* doing a
> > > > uaccess_begin(), which will mean that modern CPU's will simply fault
> > > > on a kernel access to user space.
> > >
> > > On bpf side the bpf_probe_read() helper just calls probe_kernel_read()
> > > and users pass both user and kernel addresses into it and expect
> > > that the helper will actually try to read from that address.
> >
> > Slightly related and FWIW, BCC's eBPF-based opensnoop tool [1] installs a
> > kprobe on do_sys_open to monitor calls to the open syscall globally.
> >
> > do_sys_open() has prototype:
> >
> > long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode);
> >
> > This causes a "blank" filename to be displayed by opensnoop when I run it on
> > my Pixel 3 (arm64), possibly because this is a user pointer. However, it
> > works fine on x86-64.
> >
> > So it seems to me that on arm64, reading user pointers directly still doesn't
> > work even if there is a distinction between user/kernel addresses. In that
> > case reading the user pointer using user accessors (possibly using
> > bpf_probe_user_read helper) should be needed to fix this issue (as Yonghong
> > also privately discussed with me).
>
> OK, it sounds like the same issue. Please add a bpf_user_read() and use it
> for __user pointer.
CC'd Yonghong who said eariler to me he would add it, but I could add it too
if he wants me to.
thanks,
- Joel
next prev parent reply other threads:[~2019-02-28 15:18 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 [this message]
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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