Merge branch 'regset' (PTRACE_SETREGSET data leakage)

Merge PTRACE_SETREGSET leakage fixes from Dave Martin:
 "This series is the collection of fixes I proposed on this topic, that
  have not yet appeared upstream or in the stable branches,

  The issue can leak kernel stack, but doesn't appear to allow userspace
  to attack the kernel directly.  The affected architectures are c6x,
  h8300, metag, mips and sparc.

  [ Mark Salter points out that c6x has no MMU or other mechanism to
    prevent userspace access to kernel code or data on c6x, but it
    doesn't hurt to clean that case up too. ]

  The bugs arise from use of user_regset_copyin(). Users of
  user_regset_copyin() can work in one of two ways:

   1) Copy directly to thread_struct or equivalent. (This seems to be
      the design assumption of the regset API, and is the most common
      approach.)

   2) Copy to a local variable and then transfer to thread_struct. (A
      significant minority of cases.)

  Buggy code typically involves approac...