LoongArch: BPF: Zero-extend bpf_tail_call() index

The bpf_tail_call() index should be treated as a u32 value. Let's
zero-extend it to avoid calling wrong BPF progs. See similar fixes
for x86 [1]) and arm64 ([2]) for more details.

  [1]: torvalds@90caccd
  [2]: torvalds@16338a9

Cc: stable@vger.kernel.org
Fixes: 5dc6155 ("LoongArch: Add BPF JIT support")
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: chenhengqi

arch/loongarch/net/bpf_jit.c

@@ -280,6 +280,8 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx, int insn)
 	 *	 goto out;
 	 */
 	tc_ninsn = insn ? ctx->offset[insn+1] - ctx->offset[insn] : ctx->offset[0];
+	emit_zext_32(ctx, a2, true);
+
 	off = offsetof(struct bpf_array, map.max_entries);
 	emit_insn(ctx, ldwu, t1, a1, off);
 	/* bgeu $a2, $t1, jmp_offset */