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

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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@xxxxxxxxxxx  IBM Australia Limited




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