linux-stable.git/lib/iov_iter.c, branch linux-6.8.y

iov_iter: get rid of 'copy_mc' flag

2024-03-06T09:52:12+00:00

This flag is only set by one single user: the magical core dumping code
that looks up user pages one by one, and then writes them out using
their kernel addresses (by using a BVEC_ITER).

That actually ends up being a huge problem, because while we do use
copy_mc_to_kernel() for this case and it is able to handle the possible
machine checks involved, nothing else is really ready to handle the
failures caused by the machine check.

In particular, as reported by Tong Tiangen, we don't actually support
fault_in_iov_iter_readable() on a machine check area.

As a result, the usual logic for writing things to a file under a
filesystem lock, which involves doing a copy with page faults disabled
and then if that fails trying to fault pages in without holding the
locks with fault_in_iov_iter_readable() does not work at all.

We could decide to always just make the MC copy "succeed" (and filling
the destination with zeroes), and that would then create a core dump
file that just ignores any machine checks.

But honestly, this single special case has been problematic before, and
means that all the normal iov_iter code ends up slightly more complex
and slower.

See for example commit c9eec08bac96 ("iov_iter: Don't deal with
iter->copy_mc in memcpy_from_iter_mc()") where David Howells
re-organized the code just to avoid having to check the 'copy_mc' flags
inside the inner iov_iter loops.

So considering that we have exactly one user, and that one user is a
non-critical special case that doesn't actually ever trigger in real
life (Tong found this with manual error injection), the sane solution is
to just decide that the onus on handling the machine check lines on that
user instead.

Ergo, do the copy_mc_to_kernel() in the core dump logic itself, copying
the user data to a stable kernel page before writing it out.

Fixes: f1982740f5e7 ("iov_iter: Convert iterate*() to inline funcs")
Signed-off-by: Linus Torvalds 
Signed-off-by: Tong Tiangen 
Link: https://lore.kernel.org/r/20240305133336.3804360-1-tongtiangen@huawei.com
Link: https://lore.kernel.org/all/4e80924d-9c85-f13a-722a-6a5d2b1c225a@huawei.com/
Tested-by: David Howells 
Reviewed-by: David Howells 
Reviewed-by: Jens Axboe 
Reported-by: Tong Tiangen 
Signed-off-by: Christian Brauner

Merge tag 'vfs-6.8.iov_iter' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2024-01-08T19:43:04+00:00

Pull vfs iov_iter cleanups from Christian Brauner:
 "This contains a minor cleanup. The patches drop an unused argument
  from import_single_range() allowing to replace import_single_range()
  with import_ubuf() and dropping import_single_range() completely"

* tag 'vfs-6.8.iov_iter' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  iov_iter: replace import_single_range() with import_ubuf()
  iov_iter: remove unused 'iov' argument from import_single_range()

iov_iter: replace import_single_range() with import_ubuf()

2023-12-05T10:57:37+00:00

With the removal of the 'iov' argument to import_single_range(), the two
functions are now fully identical. Convert the import_single_range()
callers to import_ubuf(), and remove the former fully.

Signed-off-by: Jens Axboe 
Link: https://lore.kernel.org/r/20231204174827.1258875-3-axboe@kernel.dk
Signed-off-by: Christian Brauner

iov_iter: remove unused 'iov' argument from import_single_range()

2023-12-05T10:57:34+00:00

It is entirely unused, just get rid of it.

Signed-off-by: Jens Axboe 
Link: https://lore.kernel.org/r/20231204174827.1258875-2-axboe@kernel.dk
Signed-off-by: Christian Brauner

iov_iter: fix copy_page_to_iter_nofault()

2023-11-18T15:42:07+00:00

The recent conversion to inline functions made two mistakes:

1. It tries to copy the full amount requested (bytes), not just what's
   available in the kmap'd page (n).
2. It's not applying the offset in the first page.

Note that copy_page_to_iter_nofault() is only used by /proc/kcore. This
was detected by drgn's test suite.

Fixes: f1982740f5e7 ("iov_iter: Convert iterate*() to inline funcs")
Signed-off-by: Omar Sandoval 
Link: https://lore.kernel.org/r/c1616e06b5248013cbbb1881bb4fef85a7a69ccb.1700257019.git.osandov@fb.com
Acked-by: David Howells 
Signed-off-by: Christian Brauner

iov_iter, net: Move hash_and_copy_to_iter() to net/

2023-10-09T07:35:14+00:00

Move hash_and_copy_to_iter() to be with its only caller in networking code.

Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/20230925120309.1731676-13-dhowells@redhat.com
cc: Alexander Viro 
cc: Jens Axboe 
cc: Christoph Hellwig 
cc: Christian Brauner 
cc: Matthew Wilcox 
cc: Linus Torvalds 
cc: David Laight 
cc: "David S. Miller" 
cc: Eric Dumazet 
cc: Jakub Kicinski 
cc: Paolo Abeni 
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
cc: netdev@vger.kernel.org
Signed-off-by: Christian Brauner

iov_iter, net: Move csum_and_copy_to/from_iter() to net/

2023-10-09T07:35:14+00:00

Move csum_and_copy_to/from_iter() to net code now that the iteration
framework can be #included.

Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/20230925120309.1731676-10-dhowells@redhat.com
cc: Alexander Viro 
cc: Jens Axboe 
cc: Christoph Hellwig 
cc: Christian Brauner 
cc: Matthew Wilcox 
cc: Linus Torvalds 
cc: David Laight 
cc: "David S. Miller" 
cc: Eric Dumazet 
cc: Jakub Kicinski 
cc: Paolo Abeni 
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
cc: netdev@vger.kernel.org
Signed-off-by: Christian Brauner

iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc()

2023-10-09T07:35:14+00:00

iter->copy_mc is only used with a bvec iterator and only by
dump_emit_page() in fs/coredump.c so rather than handle this in
memcpy_from_iter_mc() where it is checked repeatedly by _copy_from_iter()
and copy_page_from_iter_atomic(),

Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/20230925120309.1731676-9-dhowells@redhat.com
cc: Alexander Viro 
cc: Jens Axboe 
cc: Christoph Hellwig 
cc: Christian Brauner 
cc: Matthew Wilcox 
cc: Linus Torvalds 
cc: David Laight 
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: Christian Brauner

iov_iter: Convert iterate*() to inline funcs

2023-09-25T12:30:28+00:00

Convert the iov_iter iteration macros to inline functions to make the code
easier to follow.

The functions are marked __always_inline as we don't want to end up with
indirect calls in the code.  This, however, leaves dealing with ->copy_mc
in an awkard situation since the step function (memcpy_from_iter_mc())
needs to test the flag in the iterator, but isn't passed the iterator.
This will be dealt with in a follow-up patch.

The variable names in the per-type iterator functions have been harmonised
as much as possible and made clearer as to the variable purpose.

The iterator functions are also moved to a header file so that other
operations that need to scan over an iterator can be added.  For instance,
the rbd driver could use this to scan a buffer to see if it is all zeros
and libceph could use this to generate a crc.

Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/3710261.1691764329@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/855.1692047347@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/20230816120741.534415-1-dhowells@redhat.com/ # v3
Link: https://lore.kernel.org/r/20230925120309.1731676-8-dhowells@redhat.com
cc: Alexander Viro 
cc: Jens Axboe 
cc: Christoph Hellwig 
cc: Christian Brauner 
cc: Matthew Wilcox 
cc: Linus Torvalds 
cc: David Laight 
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: Christian Brauner

iov_iter: Derive user-backedness from the iterator type

2023-09-25T12:30:28+00:00

Use the iterator type to determine whether an iterator is user-backed or
not rather than using a special flag for it.  Now that ITER_UBUF and
ITER_IOVEC are 0 and 1, they can be checked with a single comparison.

Signed-off-by: David Howells 
Link: https://lore.kernel.org/r/20230925120309.1731676-7-dhowells@redhat.com
cc: Alexander Viro 
cc: Jens Axboe 
cc: Christoph Hellwig 
cc: Christian Brauner 
cc: Matthew Wilcox 
cc: Linus Torvalds 
cc: David Laight 
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: Christian Brauner