linux-kernel - Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAADnVQLCtrvvagbbkZG4PyAKb2PWzUouxG3=nxvm8QdpgEWtGQ@mail.gmail.com>
Date:   Mon, 13 Jan 2020 21:17:49 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Song Liu <songliubraving@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>,
        "joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
        "rodrigo.vivi@...el.com" <rodrigo.vivi@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "james.bottomley@...senpartnership.com" 
        <james.bottomley@...senpartnership.com>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Robert Richter <rric@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Igor Lubashev <ilubashe@...mai.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS_PERFMON
 privileged process

On Mon, Jan 13, 2020 at 7:25 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Sat, 11 Jan 2020 12:57:18 +0300
> Alexey Budankov <alexey.budankov@...ux.intel.com> wrote:
>
> >
> > On 11.01.2020 3:35, arnaldo.melo@...il.com wrote:
>
> > > Message-ID: <A7F0BF73-9189-44BA-9264-C88F2F51CBF3@...nel.org>
> > >
> > > On January 10, 2020 9:23:27 PM GMT-03:00, Song Liu <songliubraving@...com> wrote:
> > >>
> > >>
> > >>> On Jan 10, 2020, at 3:47 PM, Masami Hiramatsu <mhiramat@...nel.org>
> > >> wrote:
> > >>>
> > >>> On Fri, 10 Jan 2020 13:45:31 -0300
> > >>> Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > >>>
> > >>>> Em Sat, Jan 11, 2020 at 12:52:13AM +0900, Masami Hiramatsu escreveu:
> > >>>>> On Fri, 10 Jan 2020 15:02:34 +0100 Peter Zijlstra
> > >> <peterz@...radead.org> wrote:
> > >>>>>> Again, this only allows attaching to previously created kprobes,
> > >> it does
> > >>>>>> not allow creating kprobes, right?
> > >>>>
> > >>>>>> That is; I don't think CAP_SYS_PERFMON should be allowed to create
> > >>>>>> kprobes.
> > >>>>
> > >>>>>> As might be clear; I don't actually know what the user-ABI is for
> > >>>>>> creating kprobes.
> > >>>>
> > >>>>> There are 2 ABIs nowadays, ftrace and ebpf. perf-probe uses ftrace
> > >> interface to
> > >>>>> define new kprobe events, and those events are treated as
> > >> completely same as
> > >>>>> tracepoint events. On the other hand, ebpf tries to define new
> > >> probe event
> > >>>>> via perf_event interface. Above one is that interface. IOW, it
> > >> creates new kprobe.
> > >>>>
> > >>>> Masami, any plans to make 'perf probe' use the perf_event_open()
> > >>>> interface for creating kprobes/uprobes?
> > >>>
> > >>> Would you mean perf probe to switch to perf_event_open()?
> > >>> No, perf probe is for setting up the ftrace probe events. I think we
> > >> can add an
> > >>> option to use perf_event_open(). But current kprobe creation from
> > >> perf_event_open()
> > >>> is separated from ftrace by design.
> > >>
> > >> I guess we can extend event parser to understand kprobe directly.
> > >> Instead of
> > >>
> > >>    perf probe kernel_func
> > >>    perf stat/record -e probe:kernel_func ...
> > >>
> > >> We can just do
> > >>
> > >>    perf stat/record -e kprobe:kernel_func ...
> > >
> > >
> > > You took the words from my mouth, exactly, that is a perfect use case, an alternative to the 'perf probe' one of making a disabled event that then gets activated via record/stat/trace, in many cases it's better, removes the explicit probe setup case.
> >
> > Arnaldo, Masami, Song,
> >
> > What do you think about making this also open to CAP_SYS_PERFMON privileged processes?
> > Could you please also review and comment on patch 5/9 for bpf_trace.c?
>
> As we talked at RFC series of CAP_SYS_TRACING last year, I just expected
> to open it for enabling/disabling kprobes, not for creation.
>
> If we can accept user who has no admin priviledge but the CAP_SYS_PERFMON,
> to shoot their foot by their own risk, I'm OK to allow it. (Even though,
> it should check the max number of probes to be created by something like
> ulimit)
> I think nowadays we have fixed all such kernel crash problems on x86,
> but not sure for other archs, especially on the devices I can not reach.
> I need more help to stabilize it.

I don't see how enable/disable is any safer than creation.
If there are kernel bugs in kprobes the kernel will crash anyway.
I think such partial CAP_SYS_PERFMON would be very confusing to the users.
CAP_* is about delegation of root privileges to non-root.
Delegating some of it is ok, but disallowing creation makes it useless
for bpf tracing, so we would need to add another CAP later.
Hence I suggest to do it right away instead of breaking
sys_perf_even_open() access into two CAPs.