1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * binfmt_misc_ops handler for the selftest's fixed-interpreter case: match a 4 * 64-bit aarch64 ELF header from the prefetched buffer and route it to a fixed 5 * interpreter chosen by the program. This is the portable, self-contained 6 * equivalent of routing a foreign binary to an emulator: it matches 7 * programmatically and computes the interpreter, but points at a test binary 8 * the harness installs rather than a system emulator. 9 */ 10 #include "vmlinux.h" 11 #include <bpf/bpf_helpers.h> 12 #include <bpf/bpf_tracing.h> 13 14 char _license[] SEC("license") = "GPL"; 15 16 #define EI_CLASS 4 17 #define ELFCLASS64 2 18 #define EM_AARCH64 183 19 20 extern int bpf_binprm_set_interp(struct linux_binprm *bprm, const char *path, 21 size_t path__sz) __ksym; 22 23 /* 24 * A magic-style decision needs nothing beyond the prefetched bprm->buf, 25 * even though the match program could read the file. 26 */ 27 SEC("struct_ops.s/match") 28 bool BPF_PROG(bpf_interp_match, struct linux_binprm *bprm) 29 { 30 __u16 machine; 31 32 if (bprm->buf[0] != 0x7f || bprm->buf[1] != 'E' || 33 bprm->buf[2] != 'L' || bprm->buf[3] != 'F' || 34 bprm->buf[EI_CLASS] != ELFCLASS64) 35 return false; 36 37 /* e_machine is a 16-bit little-endian field at offset 18. */ 38 machine = (__u8)bprm->buf[18] | ((__u16)(__u8)bprm->buf[19] << 8); 39 return machine == EM_AARCH64; 40 } 41 42 SEC("struct_ops.s/load") 43 int BPF_PROG(bpf_interp_load, struct linux_binprm *bprm) 44 { 45 /* 46 * Keep the path on the (writable) stack: bpf_binprm_set_interp() takes 47 * a sized memory arg and the verifier rejects a read-only .rodata 48 * buffer for it. The harness installs the interpreter at this path. 49 */ 50 char interp[] = "/tmp/binfmt_bpf_interp"; 51 52 /* @path__sz includes the terminating NUL; 0 commits the selection. */ 53 return bpf_binprm_set_interp(bprm, interp, sizeof(interp)); 54 } 55 56 SEC(".struct_ops.link") 57 struct binfmt_misc_ops bpf_interp = { 58 .match = (void *)bpf_interp_match, 59 .load = (void *)bpf_interp_load, 60 .name = "bpf_interp", 61 }; 62