[RFC bpf-next 0/9] bpf: Add support to allocate user page

[Jiri Olsa <jolsa@kernel.org>]

hi,
we have few use cases where having the ability to allocate normal
or executable user space memory would help (like to replace function
in live process or change environment variables)

They also need writes to user memory to handle page faults, while
the existing bpf_probe_write_user() helper disables faults during
the copy.

This patchset adds the following kfuncs for sleepable uprobe programs:

  - long bpf_user_page_alloc(unsigned long nr_pages)
    allocate lazy anonymous pages in the current process

  - int bpf_user_page_exec(unsigned long addr)
    make a page readable and executable, provided it was allocated by
    bpf_user_page_alloc()

  - int bpf_probe_write_user_faultable(void __user *unsafe_dst__ign,
                                     const void *src__srcptr, u32 src__sz)
    copy data to user memory while allowing page faults to resolve the
    destination mapping.


I'm not sure it's the best way how to do this, hence the RFC post.

thanks for comments,
jirka


---
Jiri Olsa (9):
      bpf: Add __srcptr kfunc argument suffix
      bpf: Add uprobe faultable user copy kfunc
      mm: Expose locked mprotect operation
      bpf: Add kfuncs to allocate and seal user pages
      selftests/bpf: Add __srcptr kfunc arguments test
      selftests/bpf: Add user page allocation test
      selftests/bpf: Add uprobe user page exec test
      selftests/bpf: Add faultable user page writes test
      selftests/bpf: Add user page failures test

 Documentation/bpf/kfuncs.rst                               |  23 ++++
 include/linux/mm.h                                         |   3 +
 kernel/bpf/helpers.c                                       | 178 +++++++++++++++++++++++++++
 kernel/bpf/verifier.c                                      |  18 ++-
 mm/mprotect.c                                              |  20 ++-
 tools/testing/selftests/bpf/prog_tests/kfunc_call.c        |   2 +
 tools/testing/selftests/bpf/prog_tests/user_page.c         | 346 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/kfunc_call_fail.c        |  10 ++
 tools/testing/selftests/bpf/progs/kfunc_call_test.c        |  12 ++
 tools/testing/selftests/bpf/progs/user_page.c              |  61 +++++++++
 tools/testing/selftests/bpf/test_kmods/bpf_testmod.c       |   5 +
 tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h |   1 +
 12 files changed, 672 insertions(+), 7 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/user_page.c
 create mode 100644 tools/testing/selftests/bpf/progs/user_page.c