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From: Steven Rostedt <rostedt@goodmis.org>
To: Alexei Starovoitov <ast@fb.com>
Cc: <davem@davemloft.net>, <daniel@iogearbox.net>,
	<torvalds@linux-foundation.org>, <peterz@infradead.org>,
	<netdev@vger.kernel.org>, <kernel-team@fb.com>,
	<linux-api@vger.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW_TRACEPOINT
Date: Tue, 27 Mar 2018 15:07:43 -0400	[thread overview]
Message-ID: <20180327150743.4182ab3e@gandalf.local.home> (raw)
In-Reply-To: <20180327150041.3d86e16e@gandalf.local.home>

On Tue, 27 Mar 2018 15:00:41 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> >  Wasting extra 8bytes * number_of_tracepoints just for lack of trust
> > in kallsyms doesn't sound like good trade off to me.
> > If kallsyms are inaccurate all sorts of things will break:
> > kprobes, livepatch, etc.

And if kallsyms breaks, these will break by failing to attach, or some
other benign error. Ftrace uses kallsyms to find functions too, but it
only enables functions based on the result, it doesn't use the result
for anything but to compare it to what it already knows.

This is a first that I know of to trust that kallsyms returns something
that you expect to execute with no other validation. It may be valid,
but it also makes me very nervous too. If others are fine with such an
approach, then OK, we can enter a new chapter of development where we
can use kallsyms to find the functions we want to call and use it.

-- Steve

WARNING: multiple messages have this Message-ID (diff)
From: Steven Rostedt <rostedt@goodmis.org>
To: Alexei Starovoitov <ast@fb.com>
Cc: davem@davemloft.net, daniel@iogearbox.net,
	torvalds@linux-foundation.org, peterz@infradead.org,
	netdev@vger.kernel.org, kernel-team@fb.com,
	linux-api@vger.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW_TRACEPOINT
Date: Tue, 27 Mar 2018 15:07:43 -0400	[thread overview]
Message-ID: <20180327150743.4182ab3e@gandalf.local.home> (raw)
In-Reply-To: <20180327150041.3d86e16e@gandalf.local.home>

On Tue, 27 Mar 2018 15:00:41 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> >  Wasting extra 8bytes * number_of_tracepoints just for lack of trust
> > in kallsyms doesn't sound like good trade off to me.
> > If kallsyms are inaccurate all sorts of things will break:
> > kprobes, livepatch, etc.

And if kallsyms breaks, these will break by failing to attach, or some
other benign error. Ftrace uses kallsyms to find functions too, but it
only enables functions based on the result, it doesn't use the result
for anything but to compare it to what it already knows.

This is a first that I know of to trust that kallsyms returns something
that you expect to execute with no other validation. It may be valid,
but it also makes me very nervous too. If others are fine with such an
approach, then OK, we can enter a new chapter of development where we
can use kallsyms to find the functions we want to call and use it.

-- Steve

  reply	other threads:[~2018-03-27 19:07 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-27  2:46 [PATCH v6 bpf-next 00/11] bpf, tracing: introduce bpf raw tracepoints Alexei Starovoitov
2018-03-27  2:46 ` Alexei Starovoitov
2018-03-27  2:46 ` [PATCH v6 bpf-next 01/11] treewide: remove large struct-pass-by-value from tracepoint arguments Alexei Starovoitov
2018-03-27  2:46   ` Alexei Starovoitov
2018-03-27  2:46 ` [PATCH v6 bpf-next 02/11] net/mediatek: disambiguate mt76 vs mt7601u trace events Alexei Starovoitov
2018-03-27  2:46   ` Alexei Starovoitov
2018-03-27  2:46 ` [PATCH v6 bpf-next 03/11] net/mac802154: disambiguate mac80215 vs mac802154 " Alexei Starovoitov
2018-03-27  2:46   ` Alexei Starovoitov
2018-03-27  2:46 ` [PATCH v6 bpf-next 04/11] net/wireless/iwlwifi: fix iwlwifi_dev_ucode_error tracepoint Alexei Starovoitov
2018-03-27  2:46   ` Alexei Starovoitov
2018-03-27  2:47 ` [PATCH v6 bpf-next 05/11] macro: introduce COUNT_ARGS() macro Alexei Starovoitov
2018-03-27  2:47   ` Alexei Starovoitov
2018-03-27  2:47 ` [PATCH v6 bpf-next 06/11] tracepoint: compute num_args at build time Alexei Starovoitov
2018-03-27  2:47   ` Alexei Starovoitov
2018-03-27 15:15   ` Steven Rostedt
2018-03-27 15:15     ` Steven Rostedt
2018-03-27  2:47 ` [PATCH v6 bpf-next 07/11] tracepoint: introduce kernel_tracepoint_find_by_name Alexei Starovoitov
2018-03-27  2:47   ` Alexei Starovoitov
2018-03-27 14:07   ` Steven Rostedt
2018-03-27 14:07     ` Steven Rostedt
2018-03-27 14:18     ` Mathieu Desnoyers
2018-03-27 14:42       ` Steven Rostedt
2018-03-27 15:53         ` Alexei Starovoitov
2018-03-27 16:09           ` Mathieu Desnoyers
2018-03-27 16:36           ` Daniel Borkmann
2018-03-27  2:47 ` [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW_TRACEPOINT Alexei Starovoitov
2018-03-27  2:47   ` Alexei Starovoitov
2018-03-27 17:02   ` Steven Rostedt
2018-03-27 17:02     ` Steven Rostedt
2018-03-27 17:11     ` Steven Rostedt
2018-03-27 17:11       ` Steven Rostedt
2018-03-27 18:58       ` Steven Rostedt
2018-03-27 18:58         ` Steven Rostedt
2018-03-27 21:04         ` Steven Rostedt
2018-03-27 21:04           ` Steven Rostedt
2018-03-27 22:48           ` Alexei Starovoitov
2018-03-27 22:48             ` Alexei Starovoitov
2018-03-27 23:13             ` Mathieu Desnoyers
2018-03-28  0:00               ` Alexei Starovoitov
2018-03-28  0:44                 ` Mathieu Desnoyers
2018-03-28  0:51                   ` Alexei Starovoitov
2018-03-28 14:06                     ` Steven Rostedt
2018-03-27 18:45     ` Alexei Starovoitov
2018-03-27 18:45       ` Alexei Starovoitov
2018-03-27 19:00       ` Steven Rostedt
2018-03-27 19:00         ` Steven Rostedt
2018-03-27 19:07         ` Steven Rostedt [this message]
2018-03-27 19:07           ` Steven Rostedt
2018-03-27 19:10         ` Steven Rostedt
2018-03-27 19:10           ` Steven Rostedt
2018-03-27 19:10         ` Mathieu Desnoyers
2018-03-27  2:47 ` [PATCH v6 bpf-next 09/11] libbpf: add bpf_raw_tracepoint_open helper Alexei Starovoitov
2018-03-27  2:47   ` Alexei Starovoitov
2018-03-27  2:47 ` [PATCH v6 bpf-next 10/11] samples/bpf: raw tracepoint test Alexei Starovoitov
2018-03-27  2:47   ` Alexei Starovoitov
2018-03-27  2:47 ` [PATCH v6 bpf-next 11/11] selftests/bpf: test for bpf_get_stackid() from raw tracepoints Alexei Starovoitov
2018-03-27  2:47   ` Alexei Starovoitov

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