[RFC 0/4] Fix machine check recovery for copy_from_user

[Tony Luck]

Maybe this is the way forward?  I made some poor choices before
to treat poison consumption in the kernel when accessing user data
(get_user() or copy_from_user()) ... in particular assuming that
the right action was sending a SIGBUS to the task as if it had
synchronously accessed the poison location.

First three patches may need to be combined (or broken up differently)
for bisectablilty. But they are presented separately here since they
touch separate parts of the problem.

Second part is definitley incomplete. But I'd like to check that it
is the right approach before expending more brain cells in the maze
of nested macros that is lib/iov_iter.c

Last part has been posted before. It covers the case where the kernel
takes more than one swing at reading poison data before returning to
user.

Tony Luck (4):
  x86/mce: Fix copyin code to return -EFAULT on machine check.
  mce/iter: Check for copyin failure & return error up stack
  mce/copyin: fix to not SIGBUS when copying from user hits poison
  x86/mce: Avoid infinite loop for copy from user recovery

 arch/x86/kernel/cpu/mce/core.c     | 63 +++++++++++++++++++++---------
 arch/x86/kernel/cpu/mce/severity.c |  2 -
 arch/x86/lib/copy_user_64.S        | 18 +++++----
 fs/iomap/buffered-io.c             |  8 +++-
 include/linux/sched.h              |  2 +-
 include/linux/uio.h                |  2 +-
 lib/iov_iter.c                     | 15 ++++++-
 7 files changed, 77 insertions(+), 33 deletions(-)

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2.29.2