bpf: free up BPF_JMP | BPF_CALL | BPF_X opcode

free up BPF_JMP | BPF_CALL | BPF_X opcode to be used by actual
indirect call by register and use kernel internal opcode to
mark call instruction into bpf_tail_call() helper.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/arm64/net/bpf_jit_comp.c

@@ -586,7 +586,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 		break;
 	}
 	/* tail call */
-	case BPF_JMP | BPF_CALL | BPF_X:
+	case BPF_JMP | BPF_TAIL_CALL:
 		if (emit_bpf_tail_call(ctx))
 			return -EFAULT;
 		break;

arch/powerpc/net/bpf_jit_comp64.c

@@ -938,7 +938,7 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 		/*
 		 * Tail call
 		 */
-		case BPF_JMP | BPF_CALL | BPF_X:
+		case BPF_JMP | BPF_TAIL_CALL:
 			ctx->seen |= SEEN_TAILCALL;
 			bpf_jit_emit_tail_call(image, ctx, addrs[i + 1]);
 			break;

arch/s390/net/bpf_jit_comp.c

@@ -991,7 +991,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i
 		}
 		break;
 	}
-	case BPF_JMP | BPF_CALL | BPF_X:
+	case BPF_JMP | BPF_TAIL_CALL:
 		/*
 		 * Implicit input:
 		 *  B1: pointer to ctx

arch/sparc/net/bpf_jit_comp_64.c

@@ -1217,7 +1217,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 	}
 
 	/* tail call */
-	case BPF_JMP | BPF_CALL |BPF_X:
+	case BPF_JMP | BPF_TAIL_CALL:
 		emit_tail_call(ctx);
 		break;
 

arch/x86/net/bpf_jit_comp.c

@@ -877,7 +877,7 @@ xadd:			if (is_imm8(insn->off))
 			}
 			break;
 
-		case BPF_JMP | BPF_CALL | BPF_X:
+		case BPF_JMP | BPF_TAIL_CALL:
 			emit_bpf_tail_call(&prog);
 			break;
 

include/linux/filter.h

@@ -57,6 +57,9 @@ struct bpf_prog_aux;
 #define BPF_REG_AX		MAX_BPF_REG
 #define MAX_BPF_JIT_REG		(MAX_BPF_REG + 1)
 
+/* unused opcode to mark special call to bpf_tail_call() helper */
+#define BPF_TAIL_CALL	0xf0
+
 /* As per nm, we expose JITed images as text (code) section for
  * kallsyms. That way, tools like perf can find it to match
  * addresses.

kernel/bpf/core.c

@@ -824,7 +824,7 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn)
 		[BPF_ALU64 | BPF_NEG] = &&ALU64_NEG,
 		/* Call instruction */
 		[BPF_JMP | BPF_CALL] = &&JMP_CALL,
-		[BPF_JMP | BPF_CALL | BPF_X] = &&JMP_TAIL_CALL,
+		[BPF_JMP | BPF_TAIL_CALL] = &&JMP_TAIL_CALL,
 		/* Jumps */
 		[BPF_JMP | BPF_JA] = &&JMP_JA,
 		[BPF_JMP | BPF_JEQ | BPF_X] = &&JMP_JEQ_X,

kernel/bpf/verifier.c

@@ -3469,7 +3469,7 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
 			 * that doesn't support bpf_tail_call yet
 			 */
 			insn->imm = 0;
-			insn->code |= BPF_X;
+			insn->code = BPF_JMP | BPF_TAIL_CALL;
 			continue;
 		}