From mboxrd@z Thu Jan 1 00:00:00 1970 From: anton.vorontsov@linaro.org (Anton Vorontsov) Date: Fri, 13 Jul 2012 15:08:49 -0700 Subject: [PATCH 0/6] KGDB/KDB FIQ (NMI) debugger In-Reply-To: References: <20120705231034.GA16931@lizard> <20120713094954.GA12917@lizard> Message-ID: <20120713220849.GA1778@lizard> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 at gmail.com