1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * binfmt_misc_ops handler for the selftest's bound-interpreter case: one 4 * handler, one entry, an interpreter per guest architecture - each bound to 5 * a file when the entry was registered rather than to a path resolved at 6 * exec time. The load program names the one it wants; a name the entry did 7 * not bind fails the exec, which the harness checks too. 8 */ 9 #include "vmlinux.h" 10 #include <bpf/bpf_helpers.h> 11 #include <bpf/bpf_tracing.h> 12 13 char _license[] SEC("license") = "GPL"; 14 15 #define EI_CLASS 4 16 #define ELFCLASS64 2 17 #define E_MACHINE_OFF 18 18 #define EM_ARM 40 19 #define EM_AARCH64 183 20 #define EM_RISCV 243 21 22 extern int bpf_binprm_select_interp(struct linux_binprm *bprm, 23 const char *name, size_t name__sz) __ksym; 24 25 /* The guest architecture of a 64-bit ELF, or zero if it is not one. */ 26 static __u16 elf_machine(struct linux_binprm *bprm) 27 { 28 if (bprm->buf[0] != 0x7f || bprm->buf[1] != 'E' || 29 bprm->buf[2] != 'L' || bprm->buf[3] != 'F' || 30 bprm->buf[EI_CLASS] != ELFCLASS64) 31 return 0; 32 33 /* Little-endian 16-bit field, read byte-wise for the verifier. */ 34 return (__u8)bprm->buf[E_MACHINE_OFF] | 35 ((__u16)(__u8)bprm->buf[E_MACHINE_OFF + 1] << 8); 36 } 37 38 SEC("struct_ops.s/match") 39 bool BPF_PROG(interp_bind_match, struct linux_binprm *bprm) 40 { 41 __u16 machine = elf_machine(bprm); 42 43 return machine == EM_AARCH64 || machine == EM_RISCV || 44 machine == EM_ARM; 45 } 46 47 SEC("struct_ops.s/load") 48 int BPF_PROG(interp_bind_load, struct linux_binprm *bprm) 49 { 50 /* 51 * Names, not paths: each one selects a file the entry pre-opened, so 52 * nothing is resolved here or later, in any namespace. The buffers 53 * are on the stack because the verifier rejects .rodata for a sized 54 * memory argument. 55 */ 56 char first[] = "first"; 57 char second[] = "second"; 58 char unbound[] = "unbound"; 59 60 switch (elf_machine(bprm)) { 61 case EM_AARCH64: 62 return bpf_binprm_select_interp(bprm, first, sizeof(first)); 63 case EM_RISCV: 64 return bpf_binprm_select_interp(bprm, second, sizeof(second)); 65 } 66 67 /* The entry bound nothing under this name: -ENOENT fails the exec. */ 68 return bpf_binprm_select_interp(bprm, unbound, sizeof(unbound)); 69 } 70 71 SEC(".struct_ops.link") 72 struct binfmt_misc_ops interp_bind = { 73 .match = (void *)interp_bind_match, 74 .load = (void *)interp_bind_load, 75 .name = "interp_bind", 76 }; 77