From: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Aleksa Sarai <cyphar@cyphar.com>,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
"David S. Miller" <davem@davemloft.net>,
Jonathan Corbet <corbet@lwn.net>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Shuah Khan <shuah@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Brendan Gregg <bgregg@netflix.com>,
Christian Brauner <christian@brauner.io>,
Aleksa Sarai <asarai@suse.de>,
netdev@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v3 1/2] kretprobe: produce sane stack traces
Date: Sat, 3 Nov 2018 13:30:21 -0400 [thread overview]
Message-ID: <20181103133021.6676708c@vmware.local.home> (raw)
In-Reply-To: <20181104013430.9d3e91b8ebbae7dcb6860ef1@kernel.org>
On Sun, 4 Nov 2018 01:34:30 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> > I was thinking of a bitmask that represents the handlers, and use that
> > to map which handler gets called for which shadow entry for a
> > particular task.
>
> Hmm, I doubt that is too complicated and not scalable. I rather like to see
> the open shadow entry...
It can scale and not too complex (I already played a little with it).
But that said, I'm not committed to it, and using the shadow stack is
also an interesting idea.
>
> entry: [[original_retaddr][function][modified_retaddr]]
>
> So if there are many users on same function, the entries will be like this
>
> [[original_return_address][function][trampoline_A]]
> [[trampline_A][function][trampoline_B]]
> [[trampline_B][function][trampoline_C]]
>
> And on the top of the stack, there is trampline_C instead of original_return_address.
> In this case, return to trampoline_C(), it jumps back to trampline_B() and then
> it jumps back to trampline_A(). And eventually it jumps back to
> original_return_address.
Where are trampolines A, B, and C made? Do we also need to dynamically
create them? If I register multiple function tracing ones, each one
will need its own trampoline?
>
> This way, we don't need allocate another bitmap/pages for the shadow stack.
> We only need a shadow stack for each task.
> Also, unwinder can easily find the trampline_C from the shadow stack and restores
> original_return_address. (of course trampline_A,B,C must be registered so that
> search function can skip it.)
What I was thinking was to store a count and the functions to be called:
[original_return_address]
[function_A]
[function_B]
[function_C]
[ 3 ]
Then the trampoline that processes the return codes for ftrace (and
kretprobes and everyone else) can simply do:
count = pop_shadow_stack();
for (i = 0; i < count; i++) {
func = pop_shadow_stack();
func(...);
}
return_address = pop_shadow_stack();
That way we only need to register a function to the return handler and
it will be called, without worrying about making trampolines. There
will just be a single trampoline that handles all the work.
-- Steve
next prev parent reply other threads:[~2018-11-03 17:30 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 8:35 [PATCH v3 0/2] kretprobe: produce sane stack traces Aleksa Sarai
2018-11-01 8:35 ` [PATCH v3 1/2] " Aleksa Sarai
2018-11-01 15:20 ` Masami Hiramatsu
2018-11-01 21:13 ` Aleksa Sarai
2018-11-02 3:04 ` Masami Hiramatsu
2018-11-02 4:37 ` Aleksa Sarai
2018-11-03 12:47 ` Masami Hiramatsu
2018-11-02 0:47 ` Steven Rostedt
2018-11-02 5:05 ` Aleksa Sarai
2018-11-02 6:59 ` Aleksa Sarai
2018-11-02 13:16 ` Steven Rostedt
2018-11-02 15:43 ` Josh Poimboeuf
2018-11-02 16:13 ` Steven Rostedt
2018-11-03 13:00 ` Masami Hiramatsu
2018-11-03 13:13 ` Steven Rostedt
2018-11-03 16:34 ` Masami Hiramatsu
2018-11-03 17:30 ` Steven Rostedt [this message]
2018-11-03 17:33 ` Steven Rostedt
2018-11-04 2:25 ` Masami Hiramatsu
2018-11-03 7:02 ` Aleksa Sarai
2018-11-04 11:59 ` Aleksa Sarai
2018-11-06 22:15 ` Steven Rostedt
2018-11-08 7:46 ` Aleksa Sarai
2018-11-08 8:04 ` Aleksa Sarai
2018-11-08 14:44 ` Josh Poimboeuf
2018-11-09 7:26 ` Masami Hiramatsu
2018-11-09 15:10 ` Aleksa Sarai
2018-11-09 7:15 ` Masami Hiramatsu
2018-11-09 15:06 ` Aleksa Sarai
2018-11-10 15:31 ` Masami Hiramatsu
2018-11-12 10:38 ` Aleksa Sarai
2018-11-03 13:23 ` Masami Hiramatsu
2018-11-02 7:58 ` Aleksa Sarai
2018-11-02 4:01 ` kbuild test robot
2018-11-01 8:35 ` [PATCH v3 2/2] trace: remove kretprobed checks Aleksa Sarai
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