TLS offload drivers keep track of TCP seq numbers to make sure
the packets are fed into the HW in order.
When packets get dropped on the way through the stack, the driver
will get out of sync and have to use fallback encryption, but unless
TCP seq number is resynced it will never match the packets correctly
(or even worse - use incorrect record sequence number after TCP seq
wraps).
Existing drivers (mlx5) feed the entire record on every out-of-order
event, allowing FW/HW to always be in sync.
This patch adds an alternative, more akin to the RX resync. When
driver sees a frame which is past its expected sequence number the
stream must have gotten out of order (if the sequence number is
smaller than expected its likely a retransmission which doesn't
require resync). Driver will ask the stack to perform TX sync
before it submits the next full record, and fall back to software
crypto until stack has performed the sync.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
TLS offload device may lose sync with the TCP stream if packets
arrive out of order. Drivers can currently request a resync at
a specific TCP sequence number. When a record is found starting
at that sequence number kernel will inform the device of the
corresponding record number.
This requires the device to constantly scan the stream for a
known pattern (constant bytes of the header) after sync is lost.
This patch adds an alternative approach which is entirely under
the control of the kernel. Kernel tracks records it had to fully
decrypt, even though TLS socket is in TLS_HW mode. If multiple
records did not have any decrypted parts - it's a pretty strong
indication that the device is out of sync.
We choose the min number of fully encrypted records to be 2,
which should hopefully be more than will get retransmitted at
a time.
After kernel decides the device is out of sync it schedules a
resync request. If the TCP socket is empty the resync gets
performed immediately. If socket is not empty we leave the
record parser to resync when next record comes.
Before resync in message parser we peek at the TCP socket and
don't attempt the sync if the socket already has some of the
next record queued.
On resync failure (encrypted data continues to flow in) we
retry with exponential backoff, up to once every 128 records
(with a 16k record thats at most once every 2M of data).
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
It's possible that TCP stack will decide to retransmit a packet
right when that packet's data gets acked, especially in presence
of packet reordering. This means that packets may be in flight,
even though tls_device code has already freed their record state.
Make fill_sg_in() and in turn tls_sw_fallback() not generate a
warning in that case, and quietly proceed to drop such frames.
Make the exit path from tls_sw_fallback() drop monitor friendly,
for users to be able to troubleshoot dropped retransmissions.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Describe existing kernel TLS offload (added back in Linux 4.19) -
the mechanism, the expected behavior and the notable corner cases.
This documentation is mostly targeting hardware vendors who want
to implement offload, to ensure consistency between implementations.
v2:
- add emphasis around TLS_SW/TLS_HW/TLS_HW_RECORD;
- remove mentions of ongoing work (Boris);
- split the flow of data in SW vs. HW cases in TX overview
(Boris);
- call out which fields are updated by the device and which
are filled by the stack (Boris);
- move error handling into it's own section (Boris);
- add more words about fallback (Boris);
- note that checksum validation is required (Alexei);
- note that drivers shouldn't pay attention to the TLS
device features.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Dave Watson <davejwatson@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Jakub Kicinski