Re: [edk2] Corrupted EFI region

From: Matt Fleming
Date: Wed Aug 07 2013 - 16:25:00 EST

[ Adding Matthew for reals this time ]

On Wed, 07 Aug, at 09:19:08PM, Matt Fleming wrote:
> [ Readding Matthew Garrett to the Cc list, seeing as we both got removed
> for some unknown reason ]
> On Wed, 07 Aug, at 10:23:56AM, Andrew Fish wrote:
> > OK so I think I need some Cliff Notes here to help me understand what
> > is going on...
> >
> > type 4 is EfiBootServicesData and attr 0x0f is cache attributes with
> > no request for a runtime mapping. This is not runtime memory so to the
> > OS loader it is just memory EFI has used that will get freed back to
> > the OS after ExitBootServices(), along with EfiBootServicesCode,
> > EfiLoaderCode, and EfiLoaderData. The EfiLoaderCode and EfiLoaderData
> > also get freed back to the OS and they just exist for the convenience
> > of the OS loader.
> >
> > So I can't figure out why this maters? Given:
> We've seen a bunch of systems that make calls into EfiBootServicesCode
> after ExitBootServices(). There were some Apple machines in that list,
> though I don't have the details but Matthew should.
> So we map these regions unconditionally and in their original state,
> otherwise the firmware will generate fatal page faults when trying to
> access those memory regions.

Matt Fleming, Intel Open Source Technology Center
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