Re: [PATCH] hw/net: npcm7xx_emc: fix alignment to eth_hdr

[Peter Maydell]

On Thu, 27 Feb 2025 at 15:40, Patrick Venture <vent...@google.com> wrote:
>
> 'const struct eth_header', which requires 2 byte alignment
>
> Signed-off-by: Patrick Venture <vent...@google.com>
> ---
>  hw/net/npcm7xx_emc.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/hw/net/npcm7xx_emc.c b/hw/net/npcm7xx_emc.c
> index e06f652629..11ed4a9e6a 100644
> --- a/hw/net/npcm7xx_emc.c
> +++ b/hw/net/npcm7xx_emc.c
> @@ -424,7 +424,12 @@ static bool emc_can_receive(NetClientState *nc)
>  static bool emc_receive_filter1(NPCM7xxEMCState *emc, const uint8_t *buf,
>                                  size_t len, const char **fail_reason)
>  {
> -    eth_pkt_types_e pkt_type = get_eth_packet_type(PKT_GET_ETH_HDR(buf));
> +    struct eth_header eth_hdr = {};
> +    eth_pkt_types_e pkt_type;
> +
> +    memcpy(&eth_hdr, PKT_GET_ETH_HDR(buf),
> +           (sizeof(eth_hdr) > len) ? len : sizeof(eth_hdr));
> +    pkt_type = get_eth_packet_type(&eth_hdr);

Maybe better to mark struct eth_header as QEMU_PACKED?
Compare commit f8b94b4c5201 ("net: mark struct ip_header as
QEMU_PACKED"). The handling of these header structs in eth.h
is in general pretty suspect IMHO. We do the same
"get_eth_packet_type(PKT_GET_ETH_HDR(buf))" in other devices,
so this isn't just this device's bug.

thanks
-- PMM