arm64: bpf: zero upper bits after rev32

Commit d63903b ("arm64: bpf: fix endianness conversion bugs")
added upper bits zeroing to byteswap operations, but it assumes they
will be already zeroed after rev32, which is not the case on some
systems at least:

[ 9757.262607] test_bpf: #312 BSWAP 16: 0x0123456789abcdef -> 0xefcd jited:1 8 PASS
[ 9757.264435] test_bpf: #313 BSWAP 32: 0x0123456789abcdef -> 0xefcdab89 jited:1 ret 1460850314 != -271733879 (0x5712ce8a != 0xefcdab89)FAIL (1 times)
[ 9757.266260] test_bpf: #314 BSWAP 64: 0x0123456789abcdef -> 0x67452301 jited:1 8 PASS
[ 9757.268000] test_bpf: #315 BSWAP 64: 0x0123456789abcdef >> 32 -> 0xefcdab89 jited:1 8 PASS
[ 9757.269686] test_bpf: #316 BSWAP 16: 0xfedcba9876543210 -> 0x1032 jited:1 8 PASS
[ 9757.271380] test_bpf: #317 BSWAP 32: 0xfedcba9876543210 -> 0x10325476 jited:1 ret -1460850316 != 271733878 (0xa8ed3174 != 0x10325476)FAIL (1 times)
[ 9757.273022] test_bpf: #318 BSWAP 64: 0xfedcba9876543210 -> 0x98badcfe jited:1 7 PASS
[ 9757.274721] test_bpf: #319 BSWAP 64: 0xfedcba9876543210 >> 32 -> 0x10325476 jited:1 9 PASS

Fixes: d63903b ("arm64: bpf: fix endianness conversion bugs")
Signed-off-by: Artem Savkov <asavkov@redhat.com>

Author: sm00th

arch/arm64/net/bpf_jit_comp.c

@@ -944,7 +944,8 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
 			break;
 		case 32:
 			emit(A64_REV32(is64, dst, dst), ctx);
-			/* upper 32 bits already cleared */
+			/* zero-extend 32 bits into 64 bits */
+			emit(A64_UXTW(is64, dst, dst), ctx);
 			break;
 		case 64:
 			emit(A64_REV64(dst, dst), ctx);