netdev - Re: [PATCH net-next] sfc: trace_xdp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 11 Nov 2019 18:01:30 +0000
From:   Edward Cree <ecree@...arflare.com>
To:     Arthur Fabre <afabre@...udflare.com>
CC:     Solarflare linux maintainers <linux-net-drivers@...arflare.com>,
        "Charles McLachlan" <cmclachlan@...arflare.com>,
        Martin Habets <mhabets@...arflare.com>,
        David Miller <davem@...emloft.net>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Jakub Kicinski" <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        kernel-team <kernel-team@...udflare.com>
Subject: Re: [PATCH net-next] sfc: trace_xdp_exception on XDP failure

On 11/11/2019 17:38, Arthur Fabre wrote:
> On Mon, Nov 11, 2019 at 5:27 PM Edward Cree <ecree@...arflare.com> wrote:
>>
>> On 11/11/2019 10:51, Arthur Fabre wrote:
>>> diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
>>> index a7d9841105d8..5bfe1f6112a1 100644
>>> --- a/drivers/net/ethernet/sfc/rx.c
>>> +++ b/drivers/net/ethernet/sfc/rx.c
>>> @@ -678,6 +678,7 @@ static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel,
>>>                                 "XDP is not possible with multiple receive fragments (%d)\n",
>>>                                 channel->rx_pkt_n_frags);
>>>               channel->n_rx_xdp_bad_drops++;
>>> +             trace_xdp_exception(efx->net_dev, xdp_prog, xdp_act);
>>>               return false;
>>>       }
>> AIUI trace_xdp_exception() is improper here as we have not run
>>  the XDP program (and xdp_act is thus uninitialised).
>>
>> The other three, below, appear to be correct.
>> -Ed
>>
> 
> Good point. Do you know under what conditions we'd end up with
> "fragmented" packets? As far as I can tell this isn't IP
> fragmentation?

Fragments in this case means that the packet data are spread across
 multiple RX buffers (~= memory pages).  This should only happen if
 the RX packet is too big to fit in a single buffer, and when
 enabling XDP we ensure that the MTU is small enough to prevent
 that.  So in theory this can't happen if the NIC is functioning
 correctly.

-Ed