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