Messages in this thread | | | Date | Tue, 02 Oct 2012 22:27:10 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] Fix devmem_is_allowed for below 1MB accesses for an efi machine |
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On 10/02/2012 10:15 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. >
Well, we have the same in BIOS space with "reserved" regions. The problem is that they are actually I/O regions as far as programs like X, dmidecode and so on.
-hpa
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