bpf: arm64: Add support for indirect jumps

Add support for a new instruction

	BPF_JMP|BPF_X|BPF_JA, SRC=0, DST=Rx, off=0, imm=0

which does an indirect jump to a location stored in Rx.  The register
Rx should have type PTR_TO_INSN. This new type assures that the Rx
register contains a value (or a range of values) loaded from a
correct jump table – map of type instruction array.

ARM64 JIT supports indirect jumps to all registers through the A64_BR()
macro, use it to implement this new instruction.

Signed-off-by: Puranjay Mohan <[email protected]>
Reviewed-by: Anton Protopopov <[email protected]>

Author: puranjaymohan

arch/arm64/net/bpf_jit_comp.c

@@ -1452,6 +1452,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 		emit(A64_ASR(is64, dst, dst, imm), ctx);
 		break;
 
+	/* JUMP reg */
+	case BPF_JMP | BPF_JA | BPF_X:
+		emit(A64_BR(dst), ctx);
+		break;
 	/* JUMP off */
 	case BPF_JMP | BPF_JA:
 	case BPF_JMP32 | BPF_JA: