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From: Doug Anderson <dianders@chromium.org>
To: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jason Wessel <jason.wessel@windriver.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Sumit Garg <sumit.garg@linaro.org>,
	Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Will Deacon <will@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	kgdb-bugreport@lists.sourceforge.net,
	LKML <linux-kernel@vger.kernel.org>,
	Patch Tracking <patches@linaro.org>
Subject: Re: [PATCH v2 3/3] kgdb: Add NOKPROBE labels on the trap handler functions
Date: Fri, 17 Jul 2020 15:39:58 -0700	[thread overview]
Message-ID: <CAD=FV=UBMa4pt7Xg2sKXHdjo6tVaQWBQFtT_aoDJ+Xt1HrPD+Q@mail.gmail.com> (raw)
In-Reply-To: <20200716151943.2167652-4-daniel.thompson@linaro.org>

Hi,

On Thu, Jul 16, 2020 at 8:20 AM Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> Currently kgdb honours the kprobe blocklist but doesn't place its own
> trap handling code on the list. Add labels to discourage attempting to
> use kgdb to debug itself.
>
> These changes do not make it impossible to provoke recursive trapping
> since they do not cover all the calls that can be made on kgdb's entry
> logic. However going much further whilst we are sharing the kprobe
> blocklist risks reducing the capabilities of kprobe and this would be a
> bad trade off (especially so given kgdb's users are currently conditioned
> to avoid recursive traps).
>
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> ---
>  kernel/debug/debug_core.c | 8 ++++++++
>  1 file changed, 8 insertions(+)

I could just be missing something, but...

I understand not adding "NOKPROBE_SYMBOL" to generic kernel functions
that kgdb happens to call, but I'm not quite sure I understand why all
of the kdb / kgdb code itself shouldn't be in the blocklist.  I
certainly don't object to the functions you added to the blocklist, I
guess I'm must trying to understand why it's a bad idea to add more or
how you came up with the list of functions that you did.

  reply	other threads:[~2020-07-17 22:40 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-16 15:19 [PATCH v2 0/3] kgdb: Honour the kprobe blacklist when setting breakpoints Daniel Thompson
2020-07-16 15:19 ` [PATCH v2 1/3] kgdb: Honour the kprobe blocklist " Daniel Thompson
2020-07-16 20:48   ` kernel test robot
2020-07-17  8:13     ` Masami Hiramatsu
2020-07-17  8:42       ` [PATCH] kprobes: Remove show_registers() function prototype Masami Hiramatsu
2020-07-17 22:39   ` [PATCH v2 1/3] kgdb: Honour the kprobe blocklist when setting breakpoints Doug Anderson
2020-07-16 15:19 ` [PATCH v2 2/3] kgdb: Use the kprobe blocklist to limit single stepping Daniel Thompson
2020-07-17 22:39   ` Doug Anderson
2020-07-20  8:07     ` Daniel Thompson
2020-07-21 21:04       ` Doug Anderson
2020-09-04 15:22         ` Daniel Thompson
2020-07-16 15:19 ` [PATCH v2 3/3] kgdb: Add NOKPROBE labels on the trap handler functions Daniel Thompson
2020-07-17 22:39   ` Doug Anderson [this message]
2020-07-20  8:13     ` Daniel Thompson
2020-07-21 21:22       ` Doug Anderson
2020-09-04 15:40         ` Daniel Thompson
2020-07-17 13:48 ` [PATCH v2 0/3] kgdb: Honour the kprobe blacklist when setting breakpoints Masami Hiramatsu

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