man/man9/crypto_request.9

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.Dd March 27, 2020
.Dt CRYPTO_REQUEST 9
.Os
.Sh NAME
.Nm crypto_request
.Nd symmetric cryptographic operations
.Sh SYNOPSIS
.In opencrypto/cryptodev.h
.Ft int
.Fn crypto_dispatch "struct cryptop *crp"
.Ft void
.Fn crypto_freereq "struct cryptop *crp"
.Ft "struct cryptop *"
.Fn crypto_getreq "crypto_session_t cses" "int how"
.Sh DESCRIPTION
Each symmetric cryptographic operation in the kernel is described by
an instance of
.Vt struct cryptop
and is associated with an active session.
.Pp
New requests are allocated by
.Fn crypto_getreq .
.Fa cses
is a reference to an active session.
.Fa how
is passed to
.Xr malloc 9
and should be set to either
.Dv M_NOWAIT
or
.Dv M_WAITOK .
The caller should then set fields in the returned structure to describe
request-specific parameters.
Unused fields should be left as-is.
.Pp
.Fn crypto_dispatch
passes a crypto request to the driver attached to the request's session.
If there are errors in the request's fields, this function may return
an error to the caller.
If errors are encountered while servicing the request, they will instead
be reported to the request's callback function
.Pq Fa crp_callback
via
.Fa crp_etype .
.Pp
Note that a request's callback function may be invoked before
.Fn crypto_dispatch
returns.
.Pp
Once a request has signaled completion by invoking its callback function,
it should be feed via
.Fn crypto_freereq .
.Pp
Cryptographic operations include several fields to describe the request.
.Ss Buffer Types
Requests are associated with a single data buffer that is modified in place.
The type of the data buffer and the buffer itself are described by the
following fields:
.Bl -tag -width crp_buf_type
.It Fa crp_buf_type
The type of the data buffer.
The following types are supported:
.Bl -tag -width CRYPTO_BUF_CONTIG
.It Dv CRYPTO_BUF_CONTIG
An array of bytes mapped into the kernel's address space.
.It Dv CRYPTO_BUF_UIO
A scatter/gather list of kernel buffers as described in
.Xr uio 9 .
.It Dv CRYPTO_BUF_MBUF
A network memory buffer as described in
.Xr mbuf 9 .
.El
.It Fa crp_buf
A pointer to the start of a
.Dv CRYPTO_BUF_CONTIG
data buffer.
.It Fa crp_ilen
The length of a
.Dv CRYPTO_BUF_CONTIG
data buffer
.It Fa crp_mbuf
A pointer to a
.Vt struct mbuf
for
.Dv CRYPTO_BUF_MBUF .
.It Fa crp_uio
A pointer to a
.Vt struct uio
for
.Dv CRYPTO_BUF_UIO .
.It Fa crp_olen
Used with compression and decompression requests to describe the updated
length of the payload region in the data buffer.
.Pp
If a compression request increases the size of the payload,
then the data buffer is unmodified, the request completes successfully,
and
.Fa crp_olen
is set to the size the compressed data would have used.
Callers can compare this to the payload region length to determine if
the compressed data was discarded.
.El
.Ss Request Regions
Each request describes one or more regions in the data buffer using.
Each region is described by an offset relative to the start of the
data buffer and a length.
The length of some regions is the same for all requests belonging to
a session.
Those lengths are set in the session parameters of the associated
session.
All requests must define a payload region.
Other regions are only required for specific session modes.
The following regions are defined:
.Bl -column "Payload" "crp_payload_start" "crp_payload_length"
.It Sy Region Ta Sy Start Ta Sy Length Ta Sy Description
.It AAD Ta Fa crp_aad_start Ta Fa crp_aad_length Ta
Additional Authenticated Data
.It IV Ta Fa crp_iv_start Ta Fa csp_ivlen Ta
Embedded IV or nonce
.It Payload Ta Fa crp_payload_start Ta Fa crp_payload_length Ta
Data to encrypt, decrypt, compress, or decompress
.It Digest Ta Fa crp_digest_start Ta Fa csp_auth_mlen Ta
Authentication digest, hash, or tag
.El
.Pp
Requests are permitted to operate on only a subset of the data buffer.
For example,
requests from IPsec operate on network packets that include headers not
used as either additional authentication data (AAD) or payload data.
.Ss Request Operations
All requests must specify the type of operation to perform in
.Fa crp_op .
Available operations depend on the session's mode.
.Pp
Compression requests support the following operations:
.Bl -tag -width CRYPTO_OP_DECOMPRESS
.It Dv CRYPTO_OP_COMPRESS
Compress the data in the payload region of the data buffer.
.It Dv CRYPTO_OP_DECOMPRESS
Decompress the data in the payload region of the data buffer.
.El
.Pp
Cipher requests support the following operations:
.Bl -tag -width CRYPTO_OP_DECRYPT
.It Dv CRYPTO_OP_ENCRYPT
Encrypt the data in the payload region of the data buffer.
.It Dv CRYPTO_OP_DECRYPT
Decrypt the data in the payload region of the data buffer.
.El
.Pp
Digest requests support the following operations:
.Bl -tag -width CRYPTO_OP_COMPUTE_DIGEST
.It Dv CRYPTO_OP_COMPUTE_DIGEST
Calculate a digest over the payload region of the data buffer
and store the result in the digest region.
.It Dv CRYPTO_OP_VERIFY_DIGEST
Calculate a digest over the payload region of the data buffer.
Compare the calculated digest to the existing digest from the digest region.
If the digests match,
complete the request successfully.
If the digests do not match,
fail the request with
.Er EBADMSG .
.El
.Pp
AEAD and Encrypt-then-Authenticate requests support the following
operations:
.Bl -tag -width CRYPTO_OP
.It Dv CRYPTO_OP_ENCRYPT | Dv CRYPTO_OP_COMPUTE_DIGEST
Encrypt the data in the payload region of the data buffer.
Calculate a digest over the AAD and payload regions and store the
result in the data buffer.
.It Dv CRYPTO_OP_DECRYPT | Dv CRYPTO_OP_VERIFY_DIGEST
Calculate a digest over the AAD and payload regions of the data buffer.
Compare the calculated digest to the existing digest from the digest region.
If the digests match,
decrypt the payload region.
If the digests do not match,
fail the request with
.Er EBADMSG .
.El
.Ss Request IV and/or Nonce
Some cryptographic operations require an IV or nonce as an input.
An IV may be stored either in the IV region of the data buffer or in
.Fa crp_iv .
By default,
the IV is assumed to be stored in the IV region.
If the IV is stored in
.Fa crp_iv ,
.Dv CRYPTO_F_IV_SEPARATE
should be set in
.Fa crp_flags
and
.Fa crp_digest_start
should be left as zero.
.Pp
An encryption request using an IV stored in the IV region may set
.Dv CRYPTO_F_IV_GENERATE
in
.Fa crp_flags
to request that the driver generate a random IV.
Note that
.Dv CRYPTO_F_IV_GENERATE
cannot be used with decryption operations or in combination with
.Dv CRYPTO_F_IV_SEPARATE .
.Pp
Requests that store part, but not all, of the IV in the data buffer should
store the partial IV in the data buffer and pass the full IV separately in
.Fa crp_iv .
.Ss Request and Callback Scheduling
The crypto framework provides multiple methods of scheduling the dispatch
of requests to drivers along with the processing of driver callbacks.
Requests use flags in
.Fa crp_flags
to select the desired scheduling methods.
.Pp
.Fn crypto_dispatch
can pass the request to the session's driver via three different methods:
.Bl -enum
.It
The request is queued to a taskqueue backed by a pool of worker threads.
By default the pool is sized to provide one thread for each CPU.
Worker threads dequeue requests and pass them to the driver
asynchronously.
.It
The request is passed to the driver synchronously in the context of the
thread invoking
.Fn crypto_dispatch .
.It
The request is queued to a queue of pending requests.
A single worker thread dequeues requests and passes them to the driver
asynchronously.
.El
.Pp
To select the first method (taskqueue backed by multiple threads),
requests should set
.Dv CRYPTO_F_ASYNC .
To always use the third method (queue to single worker thread),
requests should set
.Dv CRYPTO_F_BATCH .
If both flags are set,
.Dv CRYPTO_F_ASYNC
takes precedence.
If neither flag is set,
.Fn crypto_dispatch
will first attempt the second method (invoke driver synchronously).
If the driver is blocked,
the request will be queued using the third method.
One caveat is that the first method is only used for requests using software
drivers which use host CPUs to process requests.
Requests whose session is associated with a hardware driver will ignore
.Dv CRYPTO_F_ASYNC
and only use
.Dv CRYPTO_F_BATCH
to determine how requests should be scheduled.
.Pp
In addition to bypassing synchronous dispatch in
.Fn crypto_dispatch ,
.Dv CRYPTO_F_BATCH
requests additional changes aimed at optimizing batches of requests to
the same driver.
When the worker thread processes a request with
.Dv CRYPTO_F_BATCH ,
it will search the pending request queue for any other requests for the same
driver,
including requests from different sessions.
If any other requests are present,
.Dv CRYPTO_HINT_MORE
is passed to the driver's process method.
Drivers may use this to batch completion interrupts.
.Pp
Callback function scheduling is simpler than request scheduling.
Callbacks can either be invoked synchronously from
.Fn crypto_done ,
or they can be queued to a pool of worker threads.
This pool of worker threads is also sized to provide one worker thread
for each CPU by default.
Note that a callback function invoked synchronously from
.Fn crypto_done
must follow the same restrictions placed on threaded interrupt handlers.
.Pp
By default,
callbacks are invoked asynchronously by a worker thread.
If
.Dv CRYPTO_F_CBIMM
is set,
the callback is always invoked synchronously from
.Fn crypto_done .
If
.Dv CRYPTO_F_CBIFSYNC
is set,
the callback is invoked synchronously if the request was processed by a
software driver or asynchronously if the request was processed by a
hardware driver.
.Pp
If a request was scheduled to the taskqueue via
.Dv CRYPTO_F_ASYNC ,
callbacks are always invoked asynchronously ignoring
.Dv CRYPTO_F_CBIMM
and
.Dv CRYPTO_F_CBIFSYNC .
In this case,
.Dv CRYPTO_F_ASYNC_KEEPORDER
may be set to ensure that callbacks for requests on a given session are
invoked in the same order that requests were queued to the session via
.Fn crypto_dispatch .
This flag is used by IPsec to ensure that decrypted network packets are
passed up the network stack in roughly the same order they were received.
.Pp
.Ss Other Request Fields
In addition to the fields and flags enumerated above,
.Vt struct cryptop
includes the following:
.Bl -tag -width crp_payload_length
.It Fa crp_session
A reference to the active session.
This is set when the request is created by
.Fn crypto_getreq
and should not be modified.
Drivers can use this to fetch driver-specific session state or
session parameters.
.It Fa crp_etype
Error status.
Either zero on success, or an error if a request fails.
Set by drivers prior to completing a request via
.Fn crypto_done .
.It Fa crp_flags
A bitmask of flags.
The following flags are available in addition to flags discussed previously:
.Bl -tag -width CRYPTO_F_DONE
.It Dv CRYPTO_F_DONE
Set by
.Fa crypto_done
before calling
.Fa crp_callback .
This flag is not very useful and will likely be removed in the future.
It can only be safely checked from the callback routine at which point
it is always set.
.El
.It Fa crp_cipher_key
Pointer to a request-specific encryption key.
If this value is not set,
the request uses the session encryption key.
.It Fa crp_auth_key
Pointer to a request-specific authentication key.
If this value is not set,
the request uses the session authentication key.
.It Fa crp_opaque
An opaque pointer.
This pointer permits users of the cryptographic framework to store
information about a request to be used in the callback.
.It Fa crp_callback
Callback function.
This must point to a callback function of type
.Vt void (*)(struct cryptop *) .
The callback function should inspect
.Fa crp_etype
to determine the status of the completed operation.
It should also arrange for the request to be freed via
.Fn crypto_freereq .
.El
.Sh RETURN VALUES
.Fn crypto_dispatch
returns an error if the request contained invalid fields,
or zero if the request was valid.
.Fn crypto_getreq
returns a pointer to a new request structure on success,
or
.Dv NULL
on failure.
.Dv NULL
can only be returned if
.Dv M_NOWAIT
was passed in
.Fa how .
.Sh SEE ALSO
.Xr ipsec 4 ,
.Xr crypto 7 ,
.Xr crypto 9 ,
.Xr crypto_session 9 ,
.Xr mbuf 9
.Xr uio 9
.Sh BUGS
Not all drivers properly handle mixing session and per-request keys
within a single session.
Consumers should either use a single key for a session specified in
the session parameters or always use per-request keys.