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SubjectRe: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine
Thank you both for the comments.

Sounds like a better solution is to allow accesses to only I/O regions
presented in the EFI memory map for physical addresses below 1 MB.

Do we need to worry about the X checksum in the first MB on an EFI system?

Thanks,
Mak.


On 10/02/2012 11:15 PM, Matthew Garrett wrote:
> On Tue, Oct 02, 2012 at 09:44:16PM -0700, H. Peter Anvin wrote:
>
>> We *always* expose the I/O regions to /dev/mem. That is what /dev/mem
>> *does*. The above is an exception (which is really obsolete, too: we
>> should simply disallow access to anything which is treated as system
>> RAM, which doesn't include the BIOS regions in question; the only reason
>> we don't is that some versions of X take a checksum of the RAM in the
>> first megabyte as some kind of idiotic random seed.)
>
> Oh, right, got you. In that case I think we potentially need a
> finer-grained check on EFI platforms - the EFI memory map is kind enough
> to tell us the difference between unusable regions and io regions, and
> we could avoid access to the unusable ones.
>



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