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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>
62 lines
1.9 KiB
C
62 lines
1.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* binfmt_misc_ops handler for the selftest's fixed-interpreter case: match a
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* 64-bit aarch64 ELF header from the prefetched buffer and route it to a fixed
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* interpreter chosen by the program. This is the portable, self-contained
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* equivalent of routing a foreign binary to an emulator: it matches
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* programmatically and computes the interpreter, but points at a test binary
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* the harness installs rather than a system emulator.
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*/
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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char _license[] SEC("license") = "GPL";
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#define EI_CLASS 4
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#define ELFCLASS64 2
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#define EM_AARCH64 183
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extern int bpf_binprm_set_interp(struct linux_binprm *bprm, const char *path,
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size_t path__sz) __ksym;
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/*
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* A magic-style decision needs nothing beyond the prefetched bprm->buf,
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* even though the match program could read the file.
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*/
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SEC("struct_ops.s/match")
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bool BPF_PROG(bpf_interp_match, struct linux_binprm *bprm)
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{
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__u16 machine;
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if (bprm->buf[0] != 0x7f || bprm->buf[1] != 'E' ||
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bprm->buf[2] != 'L' || bprm->buf[3] != 'F' ||
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bprm->buf[EI_CLASS] != ELFCLASS64)
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return false;
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/* e_machine is a 16-bit little-endian field at offset 18. */
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machine = (__u8)bprm->buf[18] | ((__u16)(__u8)bprm->buf[19] << 8);
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return machine == EM_AARCH64;
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}
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SEC("struct_ops.s/load")
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int BPF_PROG(bpf_interp_load, struct linux_binprm *bprm)
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{
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/*
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* Keep the path on the (writable) stack: bpf_binprm_set_interp() takes
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* a sized memory arg and the verifier rejects a read-only .rodata
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* buffer for it. The harness installs the interpreter at this path.
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*/
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char interp[] = "/tmp/binfmt_bpf_interp";
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/* @path__sz includes the terminating NUL; 0 commits the selection. */
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return bpf_binprm_set_interp(bprm, interp, sizeof(interp));
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}
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SEC(".struct_ops.link")
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struct binfmt_misc_ops bpf_interp = {
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.match = (void *)bpf_interp_match,
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.load = (void *)bpf_interp_load,
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.name = "bpf_interp",
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};
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