Re: [PATCH & RFC] kdump and stack overflows

[ebiederm@xmission.com (Eric W. Biederman)]

Fernando Luis Vazquez Cao <fernando@intellilink.co.jp> writes:

> On Mon, 2005-11-28 at 06:39 -0700, Eric W. Biederman wrote: 
>> Fernando Luis Vazquez Cao <fernando@intellilink.co.jp> writes:

> Regarding the stack overflow audit of the nmi path, we have the problem
> that both nmi_enter and nmi_exit in do_nmi (see code below) make heavy
> use of "current" indirectly (specially through the kernel preemption
> code).

Ok.  I wonder if it would be saner to simply replace the nmi trap
handler on the crash dump path?

>> I believe we have a separate interrupt stack that
>> should help but..
> Yes, when using 4K stacks we have a separate interrupt stack that should
> help, but I am afraid that crash dumping is about being paranoid.

Oh I agree.  If we had a private 4K stack for the nmi handler we
would not need to worry about overflow in that case.  (baring
nmi happening during nmis)  Hmm.  Is there anything to keep
us doing something bad in that case?

I guess as long as we don't clear the high bit of port 0x70 we
should be reasonably safe from the nmi firing multiple times.

Eric