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