Alex Smith d93ed09564 Improved safety for user memory accesses.
* Changed IS_USER_ADDRESS to check an address using USER_BASE and
  USER_SIZE, rather than just !IS_KERNEL_ADDRESS. The old check would
  allow user buffers to point into the physical memory map area.
* Added an unmapped hole at the end of the bottom half of the address
  space which catches buffers that cross into the uncanonical address
  region. This also removes the need to check for uncanonical return
  addresses in the syscall handler, it is no longer possible for the
  return address to be uncanonical under normal circumstances. All
  cases in which the return address might be changed by the kernel
  are still handled via the IRET path.
2012-08-02 09:32:33 +01:00
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