Re: [PATCH] hw/net: ftgmac100: copy eth_hdr for alignment

[Andrew Jeffery <andrew@codeconstruct.com.au>]

Hi Patrick,

On Thu, 2025-02-27 at 15:42 +0000, Patrick Venture wrote:
> eth_hdr requires 2 byte alignment
> 
> Signed-off-by: Patrick Venture <venture@google.com>
> ---
>  hw/net/ftgmac100.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/net/ftgmac100.c b/hw/net/ftgmac100.c
> index 1f524d7a01..a33aaa01ee 100644
> --- a/hw/net/ftgmac100.c
> +++ b/hw/net/ftgmac100.c
> @@ -989,12 +989,16 @@ static void ftgmac100_high_write(void *opaque, hwaddr addr,
>  static int ftgmac100_filter(FTGMAC100State *s, const uint8_t *buf, size_t len)
>  {
>      unsigned mcast_idx;
> +    struct eth_header eth_hdr = {};
>  
>      if (s->maccr & FTGMAC100_MACCR_RX_ALL) {
>          return 1;
>      }
>  
> -    switch (get_eth_packet_type(PKT_GET_ETH_HDR(buf))) {
> +    memcpy(&eth_hdr, PKT_GET_ETH_HDR(buf),
> +           (sizeof(eth_hdr) > len) ? len : sizeof(eth_hdr));

I don't think truncating the memcpy() in this way is what we want? The
switched value may not be meaningful for small values of len.

Perhaps return an error?

> +
> +    switch (get_eth_packet_type(&eth_hdr)) {
>      case ETH_PKT_BCAST:
>          if (!(s->maccr & FTGMAC100_MACCR_RX_BROADPKT)) {
>              return 0;
> @@ -1028,6 +1032,7 @@ static ssize_t ftgmac100_receive(NetClientState *nc, const uint8_t *buf,
>  {
>      FTGMAC100State *s = FTGMAC100(qemu_get_nic_opaque(nc));
>      FTGMAC100Desc bd;
> +    struct eth_header eth_hdr = {};
>      uint32_t flags = 0;
>      uint64_t addr;
>      uint32_t crc;
> @@ -1036,7 +1041,11 @@ static ssize_t ftgmac100_receive(NetClientState *nc, const uint8_t *buf,
>      uint32_t buf_len;
>      size_t size = len;
>      uint32_t first = FTGMAC100_RXDES0_FRS;
> -    uint16_t proto = be16_to_cpu(PKT_GET_ETH_HDR(buf)->h_proto);
> +    uint16_t proto;
> +
> +    memcpy(&eth_hdr, PKT_GET_ETH_HDR(buf),
> +           (sizeof(eth_hdr) > len) ? len : sizeof(eth_hdr));

Again here.

> +    proto = be16_to_cpu(eth_hdr.h_proto);
>      int max_frame_size = ftgmac100_max_frame_size(s, proto);
>  
>      if ((s->maccr & (FTGMAC100_MACCR_RXDMA_EN | FTGMAC100_MACCR_RXMAC_EN))
> @@ -1061,7 +1070,7 @@ static ssize_t ftgmac100_receive(NetClientState *nc, const uint8_t *buf,
>          flags |= FTGMAC100_RXDES0_FTL;
>      }
>  
> -    switch (get_eth_packet_type(PKT_GET_ETH_HDR(buf))) {
> +    switch (get_eth_packet_type(&eth_hdr)) {
>      case ETH_PKT_BCAST:
>          flags |= FTGMAC100_RXDES0_BROADCAST;
>          break;