On Tue, Feb 28, 2017 at 7:28 PM, Tom Herbert <t...@herbertland.com> wrote: > On Tue, Feb 28, 2017 at 3:22 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: >> On Tue, 2017-02-28 at 14:52 -0800, Andy Lutomirski wrote: >> >>> The user pages are a gift to the kernel. The application may not >>> modify this memory ever, otherwise the page cache and on-disk data may >>> differ. >>> >>> This is just not okay IMO. >> >> TCP works just fine in this case. >> >> TX checksum will be computed by the NIC after/while data is copied. >> >> If really the application changes the data, that will not cause any >> problems, other than user side consistency. >> >> This is why we require a copy (for all buffers that came from zero-copy) >> if network stack hits a device that can not offload TX checksum. >> >> Even pwrite() does not guarantee consistency if multiple threads are >> using it on overlapping regions. >> > The Mellanox team working on TLS offload pointed out to us that if > data is changed for a retransmit then it becomes trivial for someone > snooping to break the encryption. Sounds pretty scary and it would be > a shame if we couldn't use zero-copy in that use case :-( Hopefully we > can find a solution... >
This requires collusion by the process initiating the zerocopy send to help the entity snooping the link. That could be an attack on admin configured tunnels, but user-directed encryption offload like AF_TLS can still use zerocopy.
