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.
* 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...
The following changes since commit 2ea659a9ef488125eb46da6eb571de5eae5c43f6:
Linux 4.12-rc1 (2017-05-13 13:19:49 -0700)
are available in the git repository at:
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git uaccess-work.iov_iter
for you to fetch changes up to ea93a426af164d346a0b4fe0836143bf32177330:
iov_iter: saner checks on copyin/copyout (2017-06-29 22:29:36 -0400)
----------------------------------------------------------------
Al Viro (5):
copy_{from,to}_user(): move kasan checks and might_fault() out-of-line
copy_{to,from}_user(): consolidate object size checks
iov_iter/hardening: move object size checks to inlined part
iov_iter: sanity checks for copy to/from page primitives
iov_iter: saner checks on copyin/copyout
include/linux/thread_info.h | 27 +++++++++++++
include/linux/uaccess.h | 44 +++++----------------
include/linux/uio.h | 58 ++++++++++++++++++++++++---
lib/iov_iter.c | 96 ++++++++++++++++++++++++++++++++-------------
lib/usercopy.c | 10 ++++-
5 files changed, 167 insertions(+), 68 deletions(-)
