lkml.org 
[lkml]   [2019]   [Aug]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH net-next v2 6/9] net: macsec: hardware offloading infrastructure
    2019-08-20, 12:01:40 +0200, Antoine Tenart wrote:
    > So it seems the ability to enable or disable the offloading on a given
    > interface is the main missing feature. I'll add that, however I'll
    > probably (at least at first):
    >
    > - Have the interface to be fully offloaded or fully handled in s/w (with
    > errors being thrown if a given configuration isn't supported). Having
    > both at the same time on a given interface would be tricky because of
    > the MACsec validation parameter.
    >
    > - Won't allow to enable/disable the offloading of there are rules in
    > place, as we're not sure the same rules would be accepted by the other
    > implementation.

    That's probably quite problematic actually, because to do that you
    need to be able to resync the state between software and hardware,
    particularly packet numbers. So, yeah, we're better off having it
    completely blocked until we have a working implementation (if that
    ever happens).

    However, that means in case the user wants to set up something that's
    not offloadable, they'll have to:
    - configure the offloaded version until EOPNOTSUPP
    - tear everything down
    - restart from scratch without offloading

    That's inconvenient.

    Talking about packet numbers, can you describe how PN exhaustion is
    handled? I couldn't find much about packet numbers at all in the
    driver patches (I hope the hw doesn't wrap around from 2^32-1 to 0 on
    the same SA). At some point userspace needs to know that we're
    getting close to 2^32 and that it's time to re-key. Since the whole
    TX path of the software implementation is bypassed, it looks like the
    PN (as far as drivers/net/macsec.c is concerned) never increases, so
    userspace can't know when to negotiate a new SA.

    > I'm not sure if we should allow to mix the implementations on a given
    > physical interface (by having two MACsec interfaces attached) as the
    > validation would be impossible to do (we would have no idea if a
    > packet was correctly handled by the offloading part or just not being
    > a MACsec packet in the first place, in Rx).

    That's something that really bothers me with this proposal. Quoting
    from the commit message:

    > the packets seen by the networking stack on both the physical and
    > MACsec virtual interface are exactly the same

    If the HW/driver is expected to strip the sectag, I don't see how we
    could ever have multiple secy's at the same time and demultiplex
    properly between them. That's part of the reason why I chose to have
    virtual interfaces: without them, picking the right secy on TX gets
    weird.

    AFAICT, it means that any filters (tc, tcpdump) need to be different
    between offloaded and non-offloaded cases.

    And it's going to be confusing to the administrator when they look at
    tcpdumps expecting to see MACsec frames.

    I don't see how this implementation handles non-macsec traffic (on TX,
    that would be packets sent directly through the real interface, for
    example by wpa_supplicant - on RX, incoming MKA traffic for
    wpa_supplicant). Unless I missed something, incoming MKA traffic will
    end up on the macsec interface as well as the lower interface (not
    entirely critical, as long as wpa_supplicant can grab it on the lower
    device, but not consistent with the software implementation). How does
    the driver distinguish traffic that should pass through unmodified
    from traffic that the HW needs to encapsulate and encrypt?

    If you look at IPsec offloading, the networking stack builds up the
    ESP header, and passes the unencrypted data down to the driver. I'm
    wondering if the same would be possible with MACsec offloading: the
    macsec virtual interface adds the header (and maybe a dummy ICV), and
    then the HW does the encryption. In case of HW that needs to add the
    sectag itself, the driver would first strip the headers that the stack
    created. On receive, the driver would recreate a sectag and the macsec
    interface would just skip all verification (decrypt, PN).

    --
    Sabrina

    \
     
     \ /
      Last update: 2019-08-20 16:42    [W:3.975 / U:0.036 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site