linux-toradex.git/tools/testing/selftests/exec/binfmt_bpf_app.c, branch master Linux kernel for Apalis and Colibri modules selftests/exec: add binfmt_misc bpf-backed handler test 2026-08-03T08:08:42+00:00 Farid Zakaria farid.m.zakaria@gmail.com 2026-07-14T19:58:14+00:00 277d787feb2edeb3adae81a99fc47294d523a106 Exercise the bpf-backed ('B') binfmt_misc handlers end to end. A handler is a struct binfmt_misc_ops struct_ops map; the test loads and attaches it (which publishes it by name), activates it with a 'B' entry, and checks that a matched binary is routed to the interpreter the program selected via bpf_binprm_set_interp(). Two self-contained cases are covered: - bpf_interp: the match program matches a synthetic aarch64 ELF header from the prefetched bprm->buf and the load program routes it to a fixed interpreter of its choosing. - nix_origin: the match program parses the program headers to commit only to a "$ORIGIN/..."-relative PT_INTERP and the load program resolves it to an interpreter co-located with the binary -- the relocatable-loader case the kernel ELF loader cannot express. The relocatable binary is linked with PT_INTERP set to the literal "$ORIGIN/binfmt_bpf_interp" (-Wl,--dynamic-linker), which the kernel cannot resolve on its own. Both route to a small test interpreter that prints a marker, proving the program-selected interpreter actually ran. The bpf objects are compiled against the running kernel's BTF: the Makefile generates vmlinux.h with bpftool and the harness links libbpf. Override CLANG/BPFTOOL/VMLINUX_BTF/LIBBPF_CFLAGS/LIBBPF_LDLIBS as needed. The bpf pieces are only built when clang, bpftool, the vmlinux BTF and libbpf are all present (HAVE_BPF_TOOLCHAIN=y forces them) so the other exec selftests keep building without a bpf toolchain. Christian Brauner (Amutable) <brauner@kernel.org> says: Adapted to the two-op contract: 'B' entries carry the handler name in the interpreter field, both programs are sleepable, the match programs decide. nix_origin reads PT_INTERP from the match program and load returns zero on success. Skip on kernels without binfmt_misc_ops in BTF. Build the bpf pieces only when the toolchain is present and gitignore the generated artifacts. Signed-off-by: Farid Zakaria <farid.m.zakaria@gmail.com> Link: https://patch.msgid.link/20260714-work-bpf-binfmt_misc-v2-9-57b7529c002c@kernel.org Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org> 
Exercise the bpf-backed ('B') binfmt_misc handlers end to end. A handler
is a struct binfmt_misc_ops struct_ops map; the test loads and attaches
it (which publishes it by name), activates it with a 'B' entry, and
checks that a matched binary is routed to the interpreter the program
selected via bpf_binprm_set_interp().

Two self-contained cases are covered:

  - bpf_interp: the match program matches a synthetic aarch64 ELF header
    from the prefetched bprm->buf and the load program routes it to a
    fixed interpreter of its choosing.
  - nix_origin: the match program parses the program headers to commit
    only to a "$ORIGIN/..."-relative PT_INTERP and the load program
    resolves it to an interpreter co-located with the binary -- the
    relocatable-loader case the kernel ELF loader cannot express. The
    relocatable binary is linked with PT_INTERP set to the literal
    "$ORIGIN/binfmt_bpf_interp" (-Wl,--dynamic-linker), which the kernel
    cannot resolve on its own.

Both route to a small test interpreter that prints a marker, proving the
program-selected interpreter actually ran.

The bpf objects are compiled against the running kernel's BTF: the
Makefile generates vmlinux.h with bpftool and the harness links libbpf.
Override CLANG/BPFTOOL/VMLINUX_BTF/LIBBPF_CFLAGS/LIBBPF_LDLIBS as needed.
The bpf pieces are only built when clang, bpftool, the vmlinux BTF and
libbpf are all present (HAVE_BPF_TOOLCHAIN=y forces them) so the other
exec selftests keep building without a bpf toolchain.

Christian Brauner (Amutable) <brauner@kernel.org> says:

Adapted to the two-op contract: 'B' entries carry the handler name in
the interpreter field, both programs are sleepable, the match programs
decide. nix_origin reads PT_INTERP from the match program and load
returns zero on success. Skip on kernels without binfmt_misc_ops in BTF.
Build the bpf pieces only when the toolchain is present and gitignore
the generated artifacts.

Signed-off-by: Farid Zakaria <farid.m.zakaria@gmail.com>
Link: https://patch.msgid.link/20260714-work-bpf-binfmt_misc-v2-9-57b7529c002c@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>