[bug report] sfc: add functions to insert encap matches into the MAE

[Dan Carpenter <error27@xxxxxxxxx>]

Hello Edward Cree,

The patch 2245eb0086d8: "sfc: add functions to insert encap matches
into the MAE" from Mar 27, 2023, leads to the following Smatch static
checker warning:

	drivers/net/ethernet/sfc/mae.c:1002 efx_mae_register_encap_match()
	warn: this cast is a no-op

drivers/net/ethernet/sfc/mae.c
    953 int efx_mae_register_encap_match(struct efx_nic *efx,
    954                                  struct efx_tc_encap_match *encap)
    955 {
    956         MCDI_DECLARE_BUF(inbuf, MC_CMD_MAE_OUTER_RULE_INSERT_IN_LEN(MAE_ENC_FIELD_PAIRS_LEN));
    957         MCDI_DECLARE_BUF(outbuf, MC_CMD_MAE_OUTER_RULE_INSERT_OUT_LEN);
    958         MCDI_DECLARE_STRUCT_PTR(match_crit);
    959         size_t outlen;
    960         int rc;
    961 
    962         rc = efx_mae_encap_type_to_mae_type(encap->tun_type);
    963         if (rc < 0)
    964                 return rc;
    965         match_crit = _MCDI_DWORD(inbuf, MAE_OUTER_RULE_INSERT_IN_FIELD_MATCH_CRITERIA);
    966         /* The struct contains IP src and dst, and udp dport.
    967          * So we actually need to filter on IP src and dst, L4 dport, and
    968          * ipproto == udp.
    969          */
    970         MCDI_SET_DWORD(inbuf, MAE_OUTER_RULE_INSERT_IN_ENCAP_TYPE, rc);
    971 #ifdef CONFIG_IPV6
    972         if (encap->src_ip | encap->dst_ip) {
    973 #endif
    974                 MCDI_STRUCT_SET_DWORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_SRC_IP4_BE,
    975                                          encap->src_ip);
    976                 MCDI_STRUCT_SET_DWORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_SRC_IP4_BE_MASK,
    977                                          ~(__be32)0);
    978                 MCDI_STRUCT_SET_DWORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_DST_IP4_BE,
    979                                          encap->dst_ip);
    980                 MCDI_STRUCT_SET_DWORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_DST_IP4_BE_MASK,
    981                                          ~(__be32)0);
                                                 ^^^^^^^^^^

The __be32 is unsigned so the result is 0xffffffff and it's never sign
extented to 64 bits.

    982                 MCDI_STRUCT_SET_WORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_ETHER_TYPE_BE,
    983                                         htons(ETH_P_IP));
    984 #ifdef CONFIG_IPV6
    985         } else {
    986                 memcpy(MCDI_STRUCT_PTR(match_crit, MAE_ENC_FIELD_PAIRS_ENC_SRC_IP6_BE),
    987                        &encap->src_ip6, sizeof(encap->src_ip6));
    988                 memset(MCDI_STRUCT_PTR(match_crit, MAE_ENC_FIELD_PAIRS_ENC_SRC_IP6_BE_MASK),
    989                        0xff, sizeof(encap->src_ip6));
    990                 memcpy(MCDI_STRUCT_PTR(match_crit, MAE_ENC_FIELD_PAIRS_ENC_DST_IP6_BE),
    991                        &encap->dst_ip6, sizeof(encap->dst_ip6));
    992                 memset(MCDI_STRUCT_PTR(match_crit, MAE_ENC_FIELD_PAIRS_ENC_DST_IP6_BE_MASK),
    993                        0xff, sizeof(encap->dst_ip6));
    994                 MCDI_STRUCT_SET_WORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_ETHER_TYPE_BE,
    995                                         htons(ETH_P_IPV6));
    996         }
    997 #endif
    998         MCDI_STRUCT_SET_WORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_ETHER_TYPE_BE_MASK,
    999                                 ~(__be16)0);

But for these ones the u16 is type promoted to int and so ~0 is negative
one and will be sign extended.  The cast does nothing.

    1000         MCDI_STRUCT_SET_WORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_L4_DPORT_BE,
    1001                                 encap->udp_dport);
--> 1002         MCDI_STRUCT_SET_WORD_BE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_L4_DPORT_BE_MASK,
    1003                                 ~(__be16)0);

Same.

    1004         MCDI_STRUCT_SET_BYTE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_IP_PROTO, IPPROTO_UDP);
    1005         MCDI_STRUCT_SET_BYTE(match_crit, MAE_ENC_FIELD_PAIRS_ENC_IP_PROTO_MASK, ~0);
    1006         rc = efx_mcdi_rpc(efx, MC_CMD_MAE_OUTER_RULE_INSERT, inbuf,
    1007                           sizeof(inbuf), outbuf, sizeof(outbuf), &outlen);
    1008         if (rc)
    1009                 return rc;
    1010         if (outlen < sizeof(outbuf))
    1011                 return -EIO;
    1012         encap->fw_id = MCDI_DWORD(outbuf, MAE_OUTER_RULE_INSERT_OUT_OR_ID);
    1013         return 0;
    1014 }

regards,
dan carpenter