[PATCH V32 01/27] Add the ability to lock down access to the running kernel image

Andrew Donnellan andrew.donnellan at au1.ibm.com
Tue Apr 30 05:15:17 UTC 2019

On 29/4/19 2:54 pm, Daniel Axtens wrote:
> Hi,
>>>> I'm thinking about whether we should lock down the powerpc xmon debug
>>>> monitor - intuitively, I think the answer is yes if for no other reason
>>>> than Least Astonishment, when lockdown is enabled you probably don't
>>>> expect xmon to keep letting you access kernel memory.
>>> The original patchset contained a sysrq hotkey to allow physically
>>> present users to disable lockdown, so I'm not super concerned about
>>> this case - I could definitely be convinced otherwise, though.
> So Mimi contacted me offlist and very helpfully provided me with a much
> better and less confused justification for disabling xmon in lockdown:
> On x86, physical presence (== console access) is a trigger to
> disable/enable lockdown mode.
> In lockdown mode, you're not supposed to be able to modify memory. xmon
> allows you to modify memory, and therefore shouldn't be allowed in
> lockdown.
> So, if you can disable lockdown on the console that's probably OK, but
> it should be specifically disabling lockdown, not randomly editing
> memory with xmon.

That makes sense.

Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan at au1.ibm.com  IBM Australia Limited

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