1 files changed, 61 insertions, 0 deletions
diff --git a/tools/testing/selftests/exec/bpf_interp.bpf.c b/tools/testing/selftests/exec/bpf_interp.bpf.c
new file mode 100644
index 000000000000..8df2d2d01e25
--- /dev/null
+++ b/tools/testing/selftests/exec/bpf_interp.bpf.c
@@ -0,0 +1,61 @@
+// 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",
+};