linux-kernel - Re: [PATCH v2 1/4] bpf: Add support for reading user pointers

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Date:   Tue, 7 May 2019 01:10:45 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org,
        Michal Gregorczyk <michalgr@...e.com>,
        Adrian Ratiu <adrian.ratiu@...labora.com>,
        Mohammad Husain <russoue@...il.com>,
        Qais Yousef <qais.yousef@....com>,
        Srinivas Ramana <sramana@...eaurora.org>,
        duyuchao <yuchao.du@...soc.com>,
        Manjo Raja Rao <linux@...ojrajarao.com>,
        Karim Yaghmour <karim.yaghmour@...rsys.com>,
        Tamir Carmeli <carmeli.tamir@...il.com>,
        Yonghong Song <yhs@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Brendan Gregg <brendan.d.gregg@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Ziljstra <peterz@...radead.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>, kernel-team@...roid.com,
        bpf@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Martin KaFai Lau <kafai@...com>, netdev@...r.kernel.org,
        Song Liu <songliubraving@...com>
Subject: Re: [PATCH v2 1/4] bpf: Add support for reading user pointers

On 05/06/2019 09:57 PM, Joel Fernandes wrote:
> On Mon, May 06, 2019 at 09:11:19PM +0200, Daniel Borkmann wrote:
>> On 05/06/2019 08:31 PM, Joel Fernandes (Google) wrote:
>>> The eBPF based opensnoop tool fails to read the file path string passed
>>> to the do_sys_open function. This is because it is a pointer to
>>> userspace address and causes an -EFAULT when read with
>>> probe_kernel_read. This is not an issue when running the tool on x86 but
>>> is an issue on arm64. This patch adds a new bpf function call based
>>> which calls the recently proposed probe_user_read function [1].
>>> Using this function call from opensnoop fixes the issue on arm64.
>>>
>>> [1] https://lore.kernel.org/patchwork/patch/1051588/
>>>
>>> Cc: Michal Gregorczyk <michalgr@...e.com>
>>> Cc: Adrian Ratiu <adrian.ratiu@...labora.com>
>>> Cc: Mohammad Husain <russoue@...il.com>
>>> Cc: Qais Yousef <qais.yousef@....com>
>>> Cc: Srinivas Ramana <sramana@...eaurora.org>
>>> Cc: duyuchao <yuchao.du@...soc.com>
>>> Cc: Manjo Raja Rao <linux@...ojrajarao.com>
>>> Cc: Karim Yaghmour <karim.yaghmour@...rsys.com>
>>> Cc: Tamir Carmeli <carmeli.tamir@...il.com>
>>> Cc: Yonghong Song <yhs@...com>
>>> Cc: Alexei Starovoitov <ast@...nel.org>
>>> Cc: Brendan Gregg <brendan.d.gregg@...il.com>
>>> Cc: Masami Hiramatsu <mhiramat@...nel.org>
>>> Cc: Peter Ziljstra <peterz@...radead.org>
>>> Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
>>> Cc: Steven Rostedt <rostedt@...dmis.org>
>>> Cc: Kees Cook <keescook@...omium.org>
>>> Cc: kernel-team@...roid.com
>>> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
>>> ---
>>> Masami, could you carry these patches in the series where are you add
>>> probe_user_read function?
>>>
>>> Previous submissions is here:
>>> https://lore.kernel.org/patchwork/patch/1069552/
>>> v1->v2: split tools uapi sync into separate commit, added deprecation
>>> warning for old bpf_probe_read function.
>>
>> Please properly submit this series to bpf tree once the base
>> infrastructure from Masami is upstream.
> 
> Could you clarify what do you mean by "properly submit this series to bpf
> tree" mean? bpf@...r.kernel.org is CC'd.

Yeah, send the BPF series to bpf@...r.kernel.org once Masami's patches have
hit mainline, and we'll then route yours as fixes the usual path through
bpf tree.

>> This series here should
>> also fix up all current probe read usage under samples/bpf/ and
>> tools/testing/selftests/bpf/.
> 
> Ok. Agreed, will do that.

Great, thanks!
Daniel