bpf: expand BPF syscall with program load/unload

eBPF programs are similar to kernel modules. They are loaded by the user
process and automatically unloaded when process exits. Each eBPF program is
a safe run-to-completion set of instructions. eBPF verifier statically
determines that the program terminates and is safe to execute.

The following syscall wrapper can be used to load the program:
int bpf_prog_load(enum bpf_prog_type prog_type,
                  const struct bpf_insn *insns, int insn_cnt,
                  const char *license)
{
    union bpf_attr attr = {
        .prog_type = prog_type,
        .insns = ptr_to_u64(insns),
        .insn_cnt = insn_cnt,
        .license = ptr_to_u64(license),
    };

    return bpf(BPF_PROG_LOAD, &attr, sizeof(attr));
}
where 'insns' is an array of eBPF instructions and 'license' is a string
that must be GPL compatible to call helper functions marked gpl_only

Upon succesful load the syscall returns prog_fd.
Use close(prog_fd) to unload the program.

User space tests and examples follow in the later patches

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/bpf.h

@@ -99,12 +99,23 @@ enum bpf_cmd {
 	 * returns zero and stores next key or negative error
 	 */
 	BPF_MAP_GET_NEXT_KEY,
+
+	/* verify and load eBPF program
+	 * prog_fd = bpf(BPF_PROG_LOAD, union bpf_attr *attr, u32 size)
+	 * Using attr->prog_type, attr->insns, attr->license
+	 * returns fd or negative error
+	 */
+	BPF_PROG_LOAD,
 };
 
 enum bpf_map_type {
 	BPF_MAP_TYPE_UNSPEC,
 };
 
+enum bpf_prog_type {
+	BPF_PROG_TYPE_UNSPEC,
+};
+
 union bpf_attr {
 	struct { /* anonymous struct used by BPF_MAP_CREATE command */
 		__u32	map_type;	/* one of enum bpf_map_type */
@@ -121,6 +132,21 @@ union bpf_attr {
 			__aligned_u64 next_key;
 		};
 	};
+
+	struct { /* anonymous struct used by BPF_PROG_LOAD command */
+		__u32		prog_type;	/* one of enum bpf_prog_type */
+		__u32		insn_cnt;
+		__aligned_u64	insns;
+		__aligned_u64	license;
+	};
 } __attribute__((aligned(8)));
 
+/* integer value in 'imm' field of BPF_CALL instruction selects which helper
+ * function eBPF program intends to call
+ */
+enum bpf_func_id {
+	BPF_FUNC_unspec,
+	__BPF_FUNC_MAX_ID,
+};
+
 #endif /* _UAPI__LINUX_BPF_H__ */