linux-kernel - Re: [PATCH v3 2/3] kgdb: Add NOKPROBE labels on the trap handler functions

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Message-ID: <CAD=FV=XTgNxVLwytSY1wmCj7Dex3cWGVMA+Rkpp9gb1UN5CU_A@mail.gmail.com>
Date:   Mon, 14 Sep 2020 17:14:22 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Jason Wessel <jason.wessel@...driver.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Will Deacon <will@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        LKML <linux-kernel@...r.kernel.org>,
        Patch Tracking <patches@...aro.org>
Subject: Re: [PATCH v3 2/3] kgdb: Add NOKPROBE labels on the trap handler functions

Hi,

On Mon, Sep 14, 2020 at 6:02 AM Daniel Thompson
<daniel.thompson@...aro.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.
>
> Not every functions that executes from the trap handler needs to be
> marked up: relatively early in the trap handler execution (just after
> we bring the other CPUs to a halt) all breakpoints are replaced with
> the original opcodes. This patch marks up code in the debug_core that
> executes between trap entry and the breakpoints being deactivated
> and, also, code that executes between breakpoint activation and trap
> exit.

Other functions that seem to be missing from a quick skim:
* kgdb_io_ready()
* kgdb_roundup_cpus()
* kgdb_call_nmi_hook()

I'm not confident in my ability to spot every code path, though, so
I'm not sure at what point we stop looking.  I only spent a few
minutes and, if important, I could dig more.  Did you have any chance
to see if there was any way to have a magic linker script just add
this to everything under "kernel/debug" or something like that where
we just use a heavier hammer to whack a whole bunch?

In general any extra annotation here is better than no annotation, I
suppose.  ...so if you just want to commit what you have (maybe with
the above 3 extra functions) then I suppose it'd be fine.

-Doug


-Doug