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

[Marc-André Lureau]

Hi

On Fri, Feb 9, 2018 at 8:50 PM, Philippe Mathieu-Daudé <address@hidden> wrote:
> Hi Marc-André,
>
> On 02/09/2018 04:03 PM, Marc-André Lureau 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)
>
> I like the idea of using the ldst API and offsetof() macro,
> however I think it would be cleaner to use inlined static functions.

Could be a different patch. I don't see much reason to mix this with
the alignment fix.

Then you need to review the rest of the define too.

Thanks

>
>> +#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*/
>>
>



-- 
Marc-André Lureau