bpf: Support new 32bit offset jmp instruction

Add interpreter/jit/verifier support for 32bit offset jmp instruction.
If a conditional jmp instruction needs more than 16bit offset,
it can be simulated with a conditional jmp + a 32bit jmp insn.

Acked-by: Eduard Zingerman <[e-mail]>
Signed-off-by: Yonghong Song <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

arch/x86/net/bpf_jit_comp.c

···
 			break;
 
 		case BPF_JMP | BPF_JA:
-			if (insn->off == -1)
-				/* -1 jmp instructions will always jump
-				 * backwards two bytes. Explicitly handling
-				 * this case avoids wasting too many passes
-				 * when there are long sequences of replaced
-				 * dead code.
-				 */
-				jmp_offset = -2;
-			else
-				jmp_offset = addrs[i + insn->off] - addrs[i];
+		case BPF_JMP32 | BPF_JA:
+			if (BPF_CLASS(insn->code) == BPF_JMP) {
+				if (insn->off == -1)
+					/* -1 jmp instructions will always jump
+					 * backwards two bytes. Explicitly handling
+					 * this case avoids wasting too many passes
+					 * when there are long sequences of replaced
+					 * dead code.
+					 */
+					jmp_offset = -2;
+				else
+					jmp_offset = addrs[i + insn->off] - addrs[i];
+			} else {
+				if (insn->imm == -1)
+					jmp_offset = -2;
+				else
+					jmp_offset = addrs[i + insn->imm] - addrs[i];
+			}
 
 			if (!jmp_offset) {
 				/*

kernel/bpf/core.c

···
 {
 	const s32 off_min = S16_MIN, off_max = S16_MAX;
 	s32 delta = end_new - end_old;
-	s32 off = insn->off;
+	s32 off;
+
+	if (insn->code == (BPF_JMP32 | BPF_JA))
+		off = insn->imm;
+	else
+		off = insn->off;
 
 	if (curr < pos && curr + off + 1 >= end_old)
 		off += delta;
···
 		off -= delta;
 	if (off < off_min || off > off_max)
 		return -ERANGE;
-	if (!probe_pass)
-		insn->off = off;
+	if (!probe_pass) {
+		if (insn->code == (BPF_JMP32 | BPF_JA))
+			insn->imm = off;
+		else
+			insn->off = off;
+	}
 	return 0;
 }
 
···
 	INSN_3(JMP, JSLE, K),			\
 	INSN_3(JMP, JSET, K),			\
 	INSN_2(JMP, JA),			\
+	INSN_2(JMP32, JA),			\
 	/* Store instructions. */		\
 	/*   Register based. */			\
 	INSN_3(STX, MEM,  B),			\
···
 	}
 	JMP_JA:
 		insn += insn->off;
+		CONT;
+	JMP32_JA:
+		insn += insn->imm;
 		CONT;
 	JMP_EXIT:
 		return BPF_R0;

kernel/bpf/verifier.c

···
 			goto next;
 		if (BPF_OP(code) == BPF_EXIT || BPF_OP(code) == BPF_CALL)
 			goto next;
-		off = i + insn[i].off + 1;
+		if (code == (BPF_JMP32 | BPF_JA))
+			off = i + insn[i].imm + 1;
+		else
+			off = i + insn[i].off + 1;
 		if (off < subprog_start || off >= subprog_end) {
 			verbose(env, "jump out of range from insn %d to %d\n", i, off);
 			return -EINVAL;
···
 			 * or unconditional jump back
 			 */
 			if (code != (BPF_JMP | BPF_EXIT) &&
+			    code != (BPF_JMP32 | BPF_JA) &&
 			    code != (BPF_JMP | BPF_JA)) {
 				verbose(env, "last insn is not an exit or jmp\n");
 				return -EINVAL;
···
 static int visit_insn(int t, struct bpf_verifier_env *env)
 {
 	struct bpf_insn *insns = env->prog->insnsi, *insn = &insns[t];
-	int ret;
+	int ret, off;
 
 	if (bpf_pseudo_func(insn))
 		return visit_func_call_insn(t, insns, env, true);
···
 		if (BPF_SRC(insn->code) != BPF_K)
 			return -EINVAL;
 
+		if (BPF_CLASS(insn->code) == BPF_JMP)
+			off = insn->off;
+		else
+			off = insn->imm;
+
 		/* unconditional jump with single edge */
-		ret = push_insn(t, t + insn->off + 1, FALLTHROUGH, env,
+		ret = push_insn(t, t + off + 1, FALLTHROUGH, env,
 				true);
 		if (ret)
 			return ret;
 
-		mark_prune_point(env, t + insn->off + 1);
-		mark_jmp_point(env, t + insn->off + 1);
+		mark_prune_point(env, t + off + 1);
+		mark_jmp_point(env, t + off + 1);
 
 		return ret;
 
···
 				mark_reg_scratched(env, BPF_REG_0);
 			} else if (opcode == BPF_JA) {
 				if (BPF_SRC(insn->code) != BPF_K ||
-				    insn->imm != 0 ||
 				    insn->src_reg != BPF_REG_0 ||
 				    insn->dst_reg != BPF_REG_0 ||
-				    class == BPF_JMP32) {
+				    (class == BPF_JMP && insn->imm != 0) ||
+				    (class == BPF_JMP32 && insn->off != 0)) {
 					verbose(env, "BPF_JA uses reserved fields\n");
 					return -EINVAL;
 				}
 
-				env->insn_idx += insn->off + 1;
+				if (class == BPF_JMP)
+					env->insn_idx += insn->off + 1;
+				else
+					env->insn_idx += insn->imm + 1;
 				continue;
 
 			} else if (opcode == BPF_EXIT) {
···
 {
 	u8 op;
 
+	op = BPF_OP(code);
 	if (BPF_CLASS(code) == BPF_JMP32)
-		return true;
+		return op != BPF_JA;
 
 	if (BPF_CLASS(code) != BPF_JMP)
 		return false;
 
-	op = BPF_OP(code);
 	return op != BPF_JA && op != BPF_EXIT && op != BPF_CALL;
 }