linux-kernel - Re: [PATCH 0/6] KGDB/KDB FIQ (NMI) debugger

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Message-ID: <20120713220849.GA1778@lizard>
Date:	Fri, 13 Jul 2012 15:08:49 -0700
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Colin Cross <ccross@...roid.com>
Cc:	Russell King <linux@....linux.org.uk>,
	Jason Wessel <jason.wessel@...driver.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com, kgdb-bugreport@...ts.sourceforge.net
Subject: Re: [PATCH 0/6] KGDB/KDB FIQ (NMI) debugger

On Fri, Jul 13, 2012 at 09:43:45AM -0700, Colin Cross wrote:
[...]
> I was referring to the security implications, not size.  Leaving KDB
> on is effectively instant root access over the serial console.

Oh, I see. Yes, for this we'd need to disable all modification commands.

[...]
> > The thing is, we even have a standard sequence for entering KDB,
> > it is GDB-protocol command $3#33, so it actually makes sense to
> > implement this. This would be the only async command, and it doesn't
> > affect anything but the new code. I prepared a separate patch for this.
> 
> I would suggest making the sequence longer than just return.  A single
> character is not that unlikely to be generated by random noise - I've
> seen multiple devices reboot when the serial console was connected
> because it received a SysRq-Crash (a break is all zeroes, which is
> very common while shorting the lines as the console is plugged in, and
> then random noise sent a 'c').

No no, it's not just return. It is either return or the longer '$3#33'
escape sequence. Default is $3#33, so it should be pretty safe (but of
course we can make it even longer, or even configurable).

Thanks,

-- 
Anton Vorontsov
Email: cbouatmailru@...il.com
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