On 10/02/2012 09:31 PM, Matthew Garrett wrote: > On Tue, Oct 02, 2012 at 02:50:09PM -0700, H. Peter Anvin wrote: > >> That sounds like exactly the opposite of normal /dev/mem behavior... we >> allow access to non-memory resources (which really could do anything if >> misused), but not memory. > > From arch/x86/mm/init.c: > > * On x86, access has to be given to the first megabyte of ram because that area > * contains bios code and data regions used by X and dosemu and similar apps. > > Limiting this to just RAM would be safer than it currently is. I'm not > convinced that there's any good reason to allow *any* access down there > for EFI systems, though. > Sorry, fail. 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.) -hpa -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>