Re: [Qemu-devel] [PATCH] net: fix misaligned member access

[Peter Maydell]

On 9 February 2018 at 19:03, Marc-André Lureau
<address@hidden> wrote:
> Fixes the following ASAN warnings:
>
> /home/elmarco/src/qemu/hw/net/net_tx_pkt.c:201:27: runtime error: member 
> access within misaligned address 0x631000028846 for type 'struct ip_header', 
> which requires 4 byte alignment
> 0x631000028846: note: pointer points here
>  01 00 00 00 45 00  01 a9 01 00 00 00 40 11  78 45 00 00 00 00 ff ff  ff ff 
> 00 00 00 00 00 00  00 00
>              ^
> /home/elmarco/src/qemu/hw/net/net_tx_pkt.c:208:63: runtime error: member 
> access within misaligned address 0x631000028846 for type 'struct ip_header', 
> which requires 4 byte alignment
> 0x631000028846: note: pointer points here
>  01 00 00 00 45 00  01 a9 01 00 00 00 40 11  78 45 00 00 00 00 ff ff  ff ff 
> 00 00 00 00 00 00  00 00
>              ^
> /home/elmarco/src/qemu/hw/net/net_tx_pkt.c:210:13: runtime error: member 
> access within misaligned address 0x631000028846 for type 'struct ip_header', 
> which requires 4 byte alignment
> 0x631000028846: note: pointer points here
>  01 00 00 00 45 00  01 a9 01 00 00 00 40 11  78 45 00 00 00 00 ff ff  ff ff 
> 00 00 00 00 00 00  00 00
>
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  include/net/eth.h   | 4 +++-
>  hw/net/net_tx_pkt.c | 2 +-
>  2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/eth.h b/include/net/eth.h
> index 09054a506d..e6dc8a7ba0 100644
> --- a/include/net/eth.h
> +++ b/include/net/eth.h
> @@ -194,7 +194,9 @@ struct tcp_hdr {
>  #define PKT_GET_IP_HDR(p)         \
>      ((struct ip_header *)(((uint8_t *)(p)) + eth_get_l2_hdr_length(p)))
>  #define IP_HDR_GET_LEN(p)         \
> -    ((((struct ip_header *)(p))->ip_ver_len & 0x0F) << 2)
> +    ((ldub_p(p + offsetof(struct ip_header, ip_ver_len)) & 0x0F) << 2)
> +#define IP_HDR_GET_P(p)                                           \
> +    (ldub_p(p + offsetof(struct ip_header, ip_p)))
>  #define PKT_GET_IP_HDR_LEN(p)     \
>      (IP_HDR_GET_LEN(PKT_GET_IP_HDR(p)))
>  #define PKT_GET_IP6_HDR(p)        \
> diff --git a/hw/net/net_tx_pkt.c b/hw/net/net_tx_pkt.c
> index e29c881bc2..162f802dd7 100644
> --- a/hw/net/net_tx_pkt.c
> +++ b/hw/net/net_tx_pkt.c
> @@ -205,7 +205,7 @@ static bool net_tx_pkt_parse_headers(struct NetTxPkt *pkt)
>              return false;
>          }
>
> -        pkt->l4proto = ((struct ip_header *) l3_hdr->iov_base)->ip_p;
> +        pkt->l4proto = IP_HDR_GET_P(l3_hdr->iov_base);
>
>          if (IP_HDR_GET_LEN(l3_hdr->iov_base) != sizeof(struct ip_header)) {
>              /* copy optional IPv4 header data if any*/
> --
> 2.16.1.73.g5832b7e9f2

Reviewed-by: Peter Maydell <address@hidden>

and I'm going to apply this to master, because I'm fed up of the warnings
in my build system logs.

It looks like all these macros need to be fixed, though, not just these two.

thanks
-- PMM