MIPS: bpf: Fix PKT_TYPE case for big-endian cores

The skb->pkt_type field is defined as follows:

u8 pkt_type:3,
   fclone:2,
   ipvs_property:1,
   peeked:1,
   nf_trace:1

resulting to the following layout in big-endian systems

[pkt_type][fclone][ipvs_propery][peeked][nf_trace]
^                                                ^
|                                                |
LSB                                             MSB

As a result, the existing code did not work because it was trying to
match pkt_type == 7 whereas in reality it is 7<<5 on big-endian
systems.

This has been fixed in the interpreter in
0dcceabb0c1bf2d4c12a748df9933fad303072a7
"net: filter: fix SKF_AD_PKTTYPE extension on big-endian"

The fix is to look for 7<<5 on big-endian systems for the pkt_type
field, and shift by 5 so the packet type will be at the lower 3 bits
of the A register.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: netdev@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7132/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/net/bpf_jit.c

@@ -751,13 +751,17 @@ static u64 jit_get_skb_w(struct sk_buff *skb, unsigned offset)
 	return (u64)err << 32 | ntohl(ret);
 }
 
-#define PKT_TYPE_MAX 7
+#ifdef __BIG_ENDIAN_BITFIELD
+#define PKT_TYPE_MAX	(7 << 5)
+#else
+#define PKT_TYPE_MAX	7
+#endif
 static int pkt_type_offset(void)
 {
 	struct sk_buff skb_probe = {
 		.pkt_type = ~0,
 	};
-	char *ct = (char *)&skb_probe;
+	u8 *ct = (u8 *)&skb_probe;
 	unsigned int off;
 
 	for (off = 0; off < sizeof(struct sk_buff); off++) {
@@ -1320,6 +1324,10 @@ jmp_cmp:
 			emit_load_byte(r_tmp, r_skb, off, ctx);
 			/* Keep only the last 3 bits */
 			emit_andi(r_A, r_tmp, PKT_TYPE_MAX, ctx);
+#ifdef __BIG_ENDIAN_BITFIELD
+			/* Get the actual packet type to the lower 3 bits */
+			emit_srl(r_A, r_A, 5, ctx);
+#endif
 			break;
 		case BPF_ANC | SKF_AD_QUEUE:
 			ctx->flags |= SEEN_SKB | SEEN_A;