Merge branch 'uaccess-work.iov_iter' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull iov_iter hardening from Al Viro:
 "This is the iov_iter/uaccess/hardening pile.

  For one thing, it trims the inline part of copy_to_user/copy_from_user
  to the minimum that *does* need to be inlined - object size checks,
  basically. For another, it sanitizes the checks for iov_iter
  primitives. There are 4 groups of checks: access_ok(), might_fault(),
  object size and KASAN.

   - access_ok() had been verified by whoever had set the iov_iter up.
     However, that has happened in a function far away, so proving that
     there's no path to actual copying bypassing those checks is hard
     and proving that iov_iter has not been buggered in the meanwhile is
     also not pleasant. So we want those redone in actual
     copyin/copyout.

   - might_fault() is better off consolidated - we know whether it needs
     to be checked as soon as we enter iov_iter primitive and observe
     the iov_iter flavour. No need to wait until the copyin/copyout. The
     call chains are short enough to make sure we won't miss anything -
     in fact, it's more robust that way, since there are cases where we
     do e.g. forced fault-in before getting to copyin/copyout. It's not
     quite what we need to check (in particular, combination of
     iovec-backed and set_fs(KERNEL_DS) is almost certainly a bug, not a
     cause to skip checks), but that's for later series. For now let's
     keep might_fault().

   - KASAN checks belong in copyin/copyout - at the same level where
     other iov_iter flavours would've hit them in memcpy().

   - object size checks should apply to *all* iov_iter flavours, not
     just iovec-backed ones.

  There are two groups of primitives - one gets the kernel object
  described as pointer + size (copy_to_iter(), etc.) while another gets
  it as page + offset + size (copy_page_to_iter(), etc.)

  For the first group the checks are best done where we actually have a
  chance to find the object size. In other words, those belong in inline
  wrappers in uio.h, before calling into iov_iter.c. Same kind as we
  have for inlined part of copy_to_user().

  For the second group there is no object to look at - offset in page is
  just a number, it bears no type information. So we do them in the
  common helper called by iov_iter.c primitives of that kind. All it
  currently does is checking that we are not trying to access outside of
  the compound page; eventually we might want to add some sanity checks
  on the page involved.

  So the things we need in copyin/copyout part of iov_iter.c do not
  quite match anything in uaccess.h (we want no zeroing, we *do* want
  access_ok() and KASAN and we want no might_fault() or object size
  checks done on that level). OTOH, these needs are simple enough to
  provide a couple of helpers (static in iov_iter.c) doing just what we
  need..."

* 'uaccess-work.iov_iter' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  iov_iter: saner checks on copyin/copyout
  iov_iter: sanity checks for copy to/from page primitives
  iov_iter/hardening: move object size checks to inlined part
  copy_{to,from}_user(): consolidate object size checks
  copy_{from,to}_user(): move kasan checks and might_fault() out-of-line

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