This series is based on torvalds/master.
The series is split up like so:
- Patch 1 is a simple fixup which we should take in any case (even by itself).
- Patches 2-6 add the feature, configurable selftest support, and docs.
Why not ...?
============
- Why not /proc/[pid]/userfaultfd? The proposed use case for this is for one
process to open a userfaultfd which can intercept another process' page
faults. This seems to me like exactly what CAP_SYS_PTRACE is for, though, so I
think this use case can simply use a syscall without the powers CAP_SYS_PTRACE
grants being "too much".
- Why not use a syscall? Access to syscalls is generally controlled by
capabilities. We don't have a capability which is used for userfaultfd access
without also granting more / other permissions as well, and adding a new
capability was rejected [1].
- It's possible a LSM could be used to control access instead. I suspect
adding a brand new one just for this would be rejected, but I think some
existing ones like SELinux can be used to filter syscall access. Enabling
SELinux for large production deployments which don't already use it is
likely to be a huge undertaking though, and I don't think this use case by
itself is enough to motivate that kind of architectural change.
Changelog
=========
v3->v4:
- Picked up an Acked-by on 5/5.
- Updated cover letter to cover "why not ...".
- Refactored userfaultfd_allowed() into userfaultfd_syscall_allowed(). [Peter]
- Removed obsolete comment from a previous version. [Peter]
- Refactored userfaultfd_open() in selftest. [Peter]
- Reworded admin-guide documentation. [Mike, Peter]
- Squashed 2 commits adding /dev/userfaultfd to selftest and making selftest
configurable. [Peter]
- Added "syscall" test modifier (the default behavior) to selftest. [Peter]
v2->v3:
- Rebased onto linux-next/akpm-base, in order to be based on top of the
run_vmtests.sh refactor which was merged previously.
- Picked up some Reviewed-by's.
- Fixed ioctl definition (_IO instead of _IOWR), and stopped using
compat_ptr_ioctl since it is unneeded for ioctls which don't take a pointer.
- Removed the "handle_kernel_faults" bool, simplifying the code. The result is
logically equivalent, but simpler.
- Fixed userfaultfd selftest so it returns KSFT_SKIP appropriately.
- Reworded documentation per Shuah's feedback on v2.
- Improved example usage for userfaultfd selftest.
v1->v2:
- Add documentation update.
- Test *both* userfaultfd(2) and /dev/userfaultfd via the selftest.
[1]: https://lore.kernel.org/lkml/686276b9-4530-2045-6bd8-170e5943abe4@xxxxxxxxxxxxxxxx/T/
Axel Rasmussen (5):
selftests: vm: add hugetlb_shared userfaultfd test to run_vmtests.sh
userfaultfd: add /dev/userfaultfd for fine grained access control
userfaultfd: selftests: modify selftest to use /dev/userfaultfd
userfaultfd: update documentation to describe /dev/userfaultfd
selftests: vm: add /dev/userfaultfd test cases to run_vmtests.sh
Documentation/admin-guide/mm/userfaultfd.rst | 41 +++++++++++-
Documentation/admin-guide/sysctl/vm.rst | 3 +
fs/userfaultfd.c | 69 ++++++++++++++++----
include/uapi/linux/userfaultfd.h | 4 ++
tools/testing/selftests/vm/run_vmtests.sh | 11 +++-
tools/testing/selftests/vm/userfaultfd.c | 69 +++++++++++++++++---
6 files changed, 169 insertions(+), 28 deletions(-)
--
2.37.0.170.g444d1eabd0-goog
