[PATCHv3 bpf-next 0/8] bpf: Add user memory kfuncs

[Jiri Olsa <jolsa@kernel.org>]

hi,
BPF programs have no supported interface for creating or removing private
anonymous mappings in the current task. This limits use cases that need normal
or executable memory in a live process, such as replacing a function or
changing environment variables.

Although bpf_probe_write_user() can write to user memory, it disables page
faults during the copy and therefore cannot handle memory that needs to be
faulted in.

This series adds three sleepable kfuncs for those operations:

  - bpf_user_anon_mmap(len, prot) creates a private anonymous mapping in the
    current task and returns its address. The requested protections can include
    execute permission.

  - bpf_copy_to_user(dst, src, len, flags) copies data into the current task’s
    address space, handles page faults, and reports copy errors.

  - bpf_user_munmap(addr, len) removes a mapping.

Together, the kfuncs provide a small interface for allocating, populating,
and removing memory:

  addr = bpf_user_anon_mmap(len, prot);
  ret = bpf_copy_to_user((void *)addr, src, len, flags);
  bpf_user_munmap(addr, len);

This interface lets a BPF program perform the operations in the current task’s
address space without changing bpf_probe_write_user()’s fault behavior or
introducing a separate mapping abstraction.

thanks,
jirka


rfc: https://lore.kernel.org/bpf/20261021195759.119421-1-jolsa@kernel.org/
v1:  https://lore.kernel.org/bpf/20261029212551.56964-1-jolsa@kernel.org/
v2:  https://lore.kernel.org/bpf/20261103075916.100050-1-jolsa@kernel.org/

v3 changes:
- use Alexei's change for checking the const [Aleexi]
- drop ia32 support/hack for vm_mmap [Alexei]
- remove leftover srcptr suffix in kfunc declaration
- drop extra verifier test for non-sleepable kprobe

v2 changes:
- infer read-only from constness of a pointer instead of srcptr
  argument suffix [Andrii]
- rename bpf_user_mmap to bpf_user_anon_mmap [Andrii]
- use arch_validate_prot to validate prot argument in mmap
- add the x86 compat mmap workaround
- assorted small changes

v1 changes:
- follow vm_mmap/vm_munmap design suggested by Alexei
- allow user space write only to current process, because we don't
  have remote task use case and it simplifies security checks
- many changes in tests

---
Jiri Olsa (8):
      bpf: Honor const on generic kfunc memory arguments
      bpf: Add user memory kfuncs
      selftests/bpf: Add get_procmap_info helper
      selftests/bpf: Test const kfunc memory arguments
      selftests/bpf: Test user memory mmap kfuncs
      selftests/bpf: Test user memory page exec
      selftests/bpf: Test bpf_copy_to_user kfunc
      selftests/bpf: Test user memory kfunc errors

 Documentation/bpf/kfuncs.rst                               |  21 ++++
 kernel/bpf/helpers.c                                       | 107 ++++++++++++++++
 kernel/bpf/syscall.c                                       |  10 +-
 kernel/bpf/verifier.c                                      |  24 +++-
 tools/testing/selftests/bpf/prog_tests/kfunc_call.c        |   2 +
 tools/testing/selftests/bpf/prog_tests/user_mem.c          | 349 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/kfunc_call_fail.c        |  10 ++
 tools/testing/selftests/bpf/progs/kfunc_call_test.c        |  14 +++
 tools/testing/selftests/bpf/progs/user_mem.c               | 101 +++++++++++++++
 tools/testing/selftests/bpf/test_kmods/bpf_testmod.c       |  10 ++
 tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h |   2 +
 tools/testing/selftests/bpf/trace_helpers.c                |  38 +++++-
 tools/testing/selftests/bpf/trace_helpers.h                |   1 +
 13 files changed, 676 insertions(+), 13 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/user_mem.c
 create mode 100644 tools/testing/selftests/bpf/progs/user_mem.c