An 'F' entry whose interpreter keeps the binfmt_misc superblock alive
pins the instance that owns it forever. Cover both ways to build that:

- an interpreter on the instance's own files, control file and entry
  file alike

- and an instance used as an overlayfs lower layer.

Check that an ordinary 'F' registration still succeeds so the fix stays
honest about not changing what 'F' promises.

Link: https://patch.msgid.link/20260728-work-binfmt_misc-selfpin-v1-2-74df5daeca5b@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

The test reports its own pass and fail lines, returns a bare 4 for
KSFT_SKIP and runs both cases in one process, so a failure in the first
takes the second with it. It also open-codes the register, unregister,
file-copy and mount helpers that the tests for the upcoming transparent
and loader dispatch modes need again.

Convert it to the kselftest harness: a fixture for the common setup and
teardown, one TEST_F per case so each is reported and isolated
separately, and SKIP() for the root, BTF and binfmt_misc preconditions.
Move the helpers to a shared header on the way, with the register
helper preserving the write's errno so a caller can tell a rejected
flag combination (EINVAL) from a kernel that does not know the flag at
all. The synthetic ELF header gains an e_machine argument and uses the
elf.h constants instead of open-coded numbers.

The fixture no longer mounts bpffs. The handler is attached with
bpf_map__attach_struct_ops() and nothing is ever pinned, the mount was
carried along from a bpftool-based draft. The bpf objects are compiled
with -DBPF_NO_KFUNC_PROTOTYPES - the guard bpftool emits for exactly
this - instead of sed'ing the prototypes out of the generated
vmlinux.h. And the config fragment records the options the binfmt_misc
tests need so a merge-config kernel can run them.

No change in what is tested.

Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-7-e57866e4ae0f@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Test that checks performed by execveat(..., AT_EXECVE_CHECK) are
consistent with noexec mount points and file execute permissions.

Test that SECBIT_EXEC_RESTRICT_FILE and SECBIT_EXEC_DENY_INTERACTIVE are
inherited by child processes and that they can be pinned with the
appropriate SECBIT_EXEC_RESTRICT_FILE_LOCKED and
SECBIT_EXEC_DENY_INTERACTIVE_LOCKED bits.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20241212174223.389435-4-mic@digikod.net
Signed-off-by: Kees Cook <kees@kernel.org>