Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function

From: Dave Hansen
Date: Fri Jun 14 2019 - 17:02:30 EST

On 6/14/19 10:13 AM, Yu-cheng Yu wrote:
> On Fri, 2019-06-14 at 09:13 -0700, Dave Hansen wrote:
>> On 6/14/19 8:25 AM, Yu-cheng Yu wrote:
>>> The bitmap is very big.
>> Really? It's actually, what, 8*4096=32k, so 1/32,768th of the size of
>> the libraries legacy libraries you load? Do our crash dumps really not
>> know how to represent or deal with sparse mappings?
> Ok, even the core dump is not physically big, its size still looks odd, right?

Hell if I know.

Could you please go try this in practice so that we're designing this
thing fixing real actual problems instead of phantoms that we're

> Could this also affect how much time for GDB to load it.

I don't know. Can you go find out for sure, please?

> I have a related question:
> Do we allow the application to read the bitmap, or any fault from the
> application on bitmap pages?

We have to allow apps to read it. Otherwise they can't execute

We don't have to allow them to (popuating) fault on it. But, if we
don't, we need some kind of kernel interface to avoid the faults.