On Wed, Jul 20, 2022 at 3:16 PM Schaufler, Casey <casey.schaufler@xxxxxxxxx> wrote: > > > -----Original Message----- > > From: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > > Sent: Tuesday, July 19, 2022 12:56 PM > > To: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>; Andrew Morton > > <akpm@xxxxxxxxxxxxxxxxxxxx>; Dave Hansen > > <dave.hansen@xxxxxxxxxxxxxxx>; Dmitry V . Levin <ldv@xxxxxxxxxxxx>; Gleb > > Fotengauer-Malinovskiy <glebfm@xxxxxxxxxxxx>; Hugh Dickins > > <hughd@xxxxxxxxxx>; Jan Kara <jack@xxxxxxx>; Jonathan Corbet > > <corbet@xxxxxxx>; Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>; Mike > > Kravetz <mike.kravetz@xxxxxxxxxx>; Mike Rapoport <rppt@xxxxxxxxxx>; > > Amit, Nadav <namit@xxxxxxxxxx>; Peter Xu <peterx@xxxxxxxxxx>; > > Shuah Khan <shuah@xxxxxxxxxx>; Suren Baghdasaryan > > <surenb@xxxxxxxxxx>; Vlastimil Babka <vbabka@xxxxxxx>; zhangyi > > <yi.zhang@xxxxxxxxxx> > > Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>; linux- > > doc@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; linux- > > kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; linux- > > kselftest@xxxxxxxxxxxxxxx > > Subject: [PATCH v4 0/5] userfaultfd: add /dev/userfaultfd for fine grained > > access control > > I assume that leaving the LSM mailing list off of the CC is purely > accidental. Please, please include us in the next round. Honestly it just hadn't occurred to me, but I'm more than happy to CC it on future revisions. > > > > > 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, > > You won't know if you don't ask. Fair enough - I wonder if MM folks (Andrew, Peter, Nadav especially) would find that approach more palatable than /proc/[pid]/userfaultfd? Would it make sense from our perspective to propose a userfaultfd- or MM-specific LSM for controlling access to certain features? I remember +Andrea saying Red Hat was also interested in some kind of access control mechanism like this. Would one or the other approach be more convenient for you? > > > 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 >
