1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * binfmt_misc_ops handler for the loader-substitution case: match the 4 * marker the harness poked into the payload's e_ident padding and ask for 5 * the selected interpreter to be substituted for the binary's PT_INTERP, 6 * so the binary itself runs as a fully native exec. 7 */ 8 #include "vmlinux.h" 9 #include <bpf/bpf_helpers.h> 10 #include <bpf/bpf_tracing.h> 11 12 char _license[] SEC("license") = "GPL"; 13 14 #define EI_CLASS 4 15 #define EI_PAD 9 16 #define ELFCLASS64 2 17 18 extern int bpf_binprm_set_interp(struct linux_binprm *bprm, const char *path, 19 size_t path__sz) __ksym; 20 extern int bpf_binprm_set_flags(struct linux_binprm *bprm, 21 enum bpf_binprm_flags flags) __ksym; 22 23 SEC("struct_ops.s/match") 24 bool BPF_PROG(loader_match, struct linux_binprm *bprm) 25 { 26 if (bprm->buf[0] != 0x7f || bprm->buf[1] != 'E' || 27 bprm->buf[2] != 'L' || bprm->buf[3] != 'F' || 28 bprm->buf[EI_CLASS] != ELFCLASS64) 29 return false; 30 31 /* The harness marks the payload with "LDRTST" at EI_PAD. */ 32 return bprm->buf[EI_PAD + 0] == 'L' && bprm->buf[EI_PAD + 1] == 'D' && 33 bprm->buf[EI_PAD + 2] == 'R' && bprm->buf[EI_PAD + 3] == 'T' && 34 bprm->buf[EI_PAD + 4] == 'S' && bprm->buf[EI_PAD + 5] == 'T'; 35 } 36 37 SEC("struct_ops.s/load") 38 int BPF_PROG(loader_load, struct linux_binprm *bprm) 39 { 40 char interp[] = "/tmp/binfmt_loader_interp"; 41 int err; 42 43 err = bpf_binprm_set_flags(bprm, BPF_BINPRM_LOADER); 44 if (err) 45 return err; 46 47 /* @path__sz includes the terminating NUL; 0 commits the selection. */ 48 return bpf_binprm_set_interp(bprm, interp, sizeof(interp)); 49 } 50 51 SEC(".struct_ops.link") 52 struct binfmt_misc_ops loader = { 53 .match = (void *)loader_match, 54 .load = (void *)loader_load, 55 .name = "loader", 56 }; 57