man/man9/crypto.9

.\"	$OpenBSD: crypto.9,v 1.43 2020/03/28 13:16:09 krw Exp $
.\"
.\" The author of this man page is Angelos D. Keromytis (angelos@cis.upenn.edu)
.\"
.\" Copyright (c) 2000, 2001 Angelos D. Keromytis
.\"
.\" Permission to use, copy, and modify this software with or without fee
.\" is hereby granted, provided that this entire notice is included in
.\" all source code copies of any software which is or includes a copy or
.\" modification of this software.
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.\" THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR
.\" IMPLIED WARRANTY. IN PARTICULAR, NONE OF THE AUTHORS MAKES ANY
.\" REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE
.\" MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR
.\" PURPOSE.
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.Dd $Mdocdate: March 28 2020 $
.Dt CRYPTO_GET_DRIVERID 9
.Os
.Sh NAME
.Nm crypto_get_driverid ,
.Nm crypto_register ,
.Nm crypto_unregister ,
.Nm crypto_done ,
.Nm crypto_newsession ,
.Nm crypto_freesession ,
.Nm crypto_dispatch ,
.Nm crypto_getreq ,
.Nm crypto_freereq
.Nd API for cryptographic services in the kernel
.Sh SYNOPSIS
.In crypto/cryptodev.h
.Ft int32_t
.Fn crypto_get_driverid "u_int8_t"
.Ft int
.Fn crypto_register "u_int32_t" "int *" "int (*)(u_int32_t *, struct cryptoini *)" "int (*)(u_int64_t)" "int (*)(struct cryptop *)"
.Ft int
.Fn crypto_unregister "u_int32_t" "int"
.Ft void
.Fn crypto_done "struct cryptop *"
.Ft int
.Fn crypto_newsession "u_int64_t *" "struct cryptoini *" "int"
.Ft int
.Fn crypto_freesession "u_int64_t"
.Ft int
.Fn crypto_dispatch "struct cryptop *"
.Ft struct cryptop *
.Fn crypto_getreq "int"
.Ft void
.Fn crypto_freereq "struct cryptop *"
.Bd -literal

#define EALG_MAX_BLOCK_LEN      16

struct cryptoini {
	int                cri_alg;
	int                cri_klen;
	int                cri_rnd;
	caddr_t            cri_key;
	u_int8_t           cri_iv[EALG_MAX_BLOCK_LEN];
	struct cryptoini  *cri_next;
};

struct cryptodesc {
	int                crd_skip;
	int                crd_len;
	int                crd_inject;
	int                crd_flags;
	struct cryptoini   CRD_INI;
	struct cryptodesc *crd_next;
};

struct cryptop {
	u_int64_t          crp_sid;
	int                crp_ilen;
	int                crp_olen;
	int                crp_alloctype;
	int                crp_etype;
	int                crp_flags;
	void              *crp_buf;
	void              *crp_opaque;
	struct cryptodesc *crp_desc;
	int              (*crp_callback)(struct cryptop *);
	struct cryptop    *crp_next;
	caddr_t            crp_mac;
};
.Ed
.Sh DESCRIPTION
.Nm
is a framework for drivers of cryptographic hardware to register with
the kernel so
.Dq consumers
(other kernel subsystems, and eventually
users through an appropriate device) are able to make use of it.
Drivers register with the framework the algorithms they support,
and provide entry points (functions) the framework may call to
establish, use, and tear down sessions.
Sessions are used to cache cryptographic information in a particular driver
(or associated hardware), so initialization is not needed with every request.
Consumers of cryptographic services pass a set of
descriptors that instruct the framework (and the drivers registered
with it) of the operations that should be applied on the data (more
than one cryptographic operation can be requested).
.Pp
Since the consumers may not be associated with a process, drivers may
not use
.Xr tsleep 9 .
The same holds for the framework.
Thus, a callback mechanism is used
to notify a consumer that a request has been completed (the
callback is specified by the consumer on a per-request basis).
The callback is invoked by the framework whether the request was
successfully completed or not.
An error indication is provided in the latter case.
A specific error code,
.Er EAGAIN ,
is used to indicate that a session number has changed and that the
request may be re-submitted immediately with the new session number.
Errors are only returned to the invoking function if not
enough information to call the callback is available (meaning, there
was a fatal error in verifying the arguments).
For session initialization and teardown there is no callback mechanism used.
.Pp
The
.Fn crypto_newsession
routine is called by consumers of cryptographic services (such as the
.Xr ipsec 4
stack) that wish to establish a new session with the framework.
On success, the first argument will contain the Session Identifier (SID).
The second argument contains all the necessary information for
the driver to establish the session.
The third argument indicates whether a
hardware driver should be used (1) or not (0).
The various fields in the
.Fa cryptoini
structure are:
.Bl -tag -width foobarmoocow
.It Fa cri_alg
Contains an algorithm identifier.
Currently supported encryption algorithms are:
.Bd -literal
CRYPTO_3DES_CBC
CRYPTO_BLF_CBC
CRYPTO_CAST_CBC
CRYPTO_AES_CBC
CRYPTO_AES_CTR
CRYPTO_AES_XTS
.Ed
.Pp
Authentication algorithms are:
.Bd -literal
CRYPTO_MD5_HMAC
CRYPTO_SHA1_HMAC
CRYPTO_RIPEMD160_HMAC
CRYPTO_SHA2_256_HMAC
CRYPTO_SHA2_384_HMAC
CRYPTO_SHA2_512_HMAC
.Ed
.Pp
Algorithms performing authenticated encryption are:
.Bd -literal
CRYPTO_AES_GCM_16
CRYPTO_AES_GMAC
CRYPTO_CHACHA20_POLY1305
.Ed
.It Fa cri_klen
Specifies the length of the key in bits, for variable-size key
algorithms.
.It Fa cri_rnd
Specifies the number of rounds to be used with the algorithm, for
variable-round algorithms.
.It Fa cri_key
Contains the key to be used with the algorithm.
.It Fa cri_iv
Contains an explicit initialization vector (IV), if it does not prefix
the data.
This field is ignored during initialization.
If no IV is explicitly passed (see below on details), a random IV is used
by the device driver processing the request.
.Pp
In the case of the CRYPTO_AES_XTS transform, the IV should be provided
as a 64-bit block number in host byte order.
.It Fa cri_next
Contains a pointer to another
.Fa cryptoini
structure.
Multiple such structures may be linked to establish multi-algorithm sessions
.Pf ( Xr ipsec 4
is an example consumer of such a feature).
.El
.Pp
The
.Fa cryptoini
structure and its contents will not be modified by the framework (or
the drivers used).
Subsequent requests for processing that use the
SID returned will avoid the cost of re-initializing the hardware (in
essence, SID acts as an index in the session cache of the driver).
.Pp
.Fn crypto_freesession
is called with the SID returned by
.Fn crypto_newsession
to disestablish the session.
.Pp
.Fn crypto_dispatch
is called to process a request.
The various fields in the
.Fa cryptop
structure are:
.Bl -tag -width crp_alloctype
.It Fa crp_sid
Contains the SID.
.It Fa crp_ilen
Indicates the total length in bytes of the buffer to be processed.
.It Fa crp_olen
On return, contains the length of the result, not including
.Fa crd_skip .
For symmetric crypto operations, this will be the same as the input length.
.It Fa crp_alloctype
Indicates the type of buffer, as used in the kernel
.Xr malloc 9
routine.
This will be used if the framework needs to allocate a new
buffer for the result (or for re-formatting the input).
.It Fa crp_callback
This routine is invoked upon completion of the request, whether
successful or not.
It is invoked through the
.Fn crypto_done
routine.
If the request was not successful, an error code is set in the
.Fa crp_etype
field.
It is the responsibility of the callback routine to set the appropriate
.Xr spl 9
level.
.It Fa crp_etype
Contains the error type, if any errors were encountered, or zero if
the request was successfully processed.
If the
.Er EAGAIN
error code is returned, the SID has changed (and has been recorded in the
.Fa crp_sid
field).
The consumer should record the new SID and use it in all subsequent requests.
In this case, the request may be re-submitted immediately.
This mechanism is used by the framework to perform
session migration (move a session from one driver to another, because
of availability, performance, or other considerations).
.Pp
Note that this field only makes sense when examined by
the callback routine specified in
.Fa crp_callback .
Errors are returned to the invoker of
.Fn crypto_process
only when enough information is not present to call the callback
routine (i.e., if the pointer passed is
.Dv NULL
or if no callback routine was specified).
.It Fa crp_flags
Is a bitmask of flags associated with this request.
Currently defined flags are:
.Bl -tag -width CRYPTO_F_IMBUF
.It Dv CRYPTO_F_IMBUF
The buffer pointed to by
.Fa crp_buf
is an mbuf chain.
.El
.It Fa crp_buf
Points to the input buffer.
On return (when the callback is invoked),
it contains the result of the request.
The input buffer may be an mbuf
chain or a struct uio depending on
.Fa crp_flags .
.It Fa crp_opaque
This is passed through the crypto framework untouched and is
intended for the invoking application's use.
.It Fa crp_desc
This is a linked list of descriptors.
Each descriptor provides
information about what type of cryptographic operation should be done
on the input buffer.
The various fields are:
.Bl -tag -width "crd_inject"
.It Fa crd_skip
The offset in the input buffer where processing should start.
.It Fa crd_len
How many bytes, after
.Fa crd_skip ,
should be processed.
.It Fa crd_inject
Offset from the beginning of the buffer to insert any results.
For encryption algorithms, this is where the initialization vector
(IV) will be inserted when encrypting or where it can be found when
decrypting (subject to
.Fa crd_flags ) .
For MAC algorithms, this is where the result of the keyed hash will be
inserted.
.It Fa crd_flags
The following flags are defined:
.Bl -tag -width CRD_F_IV_EXPLICIT
.It Dv CRD_F_ENCRYPT
For encryption algorithms, this bit is set when encryption is required
(when not set, decryption is performed).
.It Dv CRD_F_IV_PRESENT
For encryption algorithms, this bit is set when the IV already
precedes the data, so the
.Fa crd_inject
value will be ignored and no IV will be written in the buffer.
Otherwise, the IV used to encrypt the packet will be written
at the location pointed to by
.Fa crd_inject .
The IV length is assumed to be equal to the blocksize of the
encryption algorithm.
Some applications that do special
.Dq IV cooking ,
such as the half-IV mode in
.Xr ipsec 4 ,
can use this flag to indicate that the IV should not be written on the packet.
This flag is typically used in conjunction with the
.Dv CRD_F_IV_EXPLICIT
flag.
.It Dv CRD_F_IV_EXPLICIT
For encryption algorithms, this bit is set when the IV is explicitly
provided by the consumer in the
.Fa crd_iv
fields.
Otherwise, for encryption operations the IV is provided for by
the driver used to perform the operation, whereas for decryption
operations it is pointed to by the
.Fa crd_inject
field.
This flag is typically used when the IV is calculated
.Dq on the fly
by the consumer, and does not precede the data (some
.Xr ipsec 4
configurations, and the encrypted swap are two such examples).
.It Dv CRD_F_COMP
For compression algorithms, this bit is set when compression is required (when
not set, decompression is performed).
.El
.It Fa CRD_INI
This
.Fa cryptoini
structure will not be modified by the framework or the device drivers.
Since this information accompanies every cryptographic
operation request, drivers may re-initialize state on-demand
(typically an expensive operation).
Furthermore, the cryptographic
framework may re-route requests as a result of full queues or hardware
failure, as described above.
.It Fa crd_next
Point to the next descriptor.
Linked operations are useful in protocols such as
.Xr ipsec 4 ,
where multiple cryptographic transforms may be applied on the same
block of data.
.El
.El
.Pp
.Fn crypto_getreq
allocates a
.Fa cryptop
structure with a linked list of as many
.Fa cryptodesc
structures as were specified in the argument passed to it.
.Pp
.Fn crypto_freereq
deallocates a structure
.Fa cryptop
and any
.Fa cryptodesc
structures linked to it.
Note that it is the responsibility of the
callback routine to do the necessary cleanups associated with the
opaque field in the
.Fa cryptop
structure.
.Sh DRIVER-SIDE API
The
.Fn crypto_get_driverid ,
.Fn crypto_register ,
.Fn crypto_unregister ,
and
.Fn crypto_done
routines are used by drivers that provide support for cryptographic
primitives to register and unregister with the kernel crypto services
framework.
Drivers must first use the
.Fn crypto_get_driverid
function to acquire a driver identifier, specifying the
.Fa cc_flags
as an argument (normally 0, but software-only drivers should specify
.Dv CRYPTOCAP_F_SOFTWARE ) .
For each algorithm the driver supports, it must then call
.Fn crypto_register .
The first argument is the driver identifier.
The second argument is an array of
.Dv CRYPTO_ALGORITHM_MAX + 1
elements, indicating which algorithms are supported.
The last three arguments are pointers to three
driver-provided functions that the framework may call to establish new
cryptographic context with the driver, free already established
context, and ask for a request to be processed (encrypt, decrypt, etc.\&)
.Fn crypto_unregister
is called by drivers that wish to withdraw support for an algorithm.
The two arguments are the driver and algorithm identifiers, respectively.
Typically, drivers for
.Xr pcmcia 4
crypto cards that are being ejected will invoke this routine for all
algorithms supported by the card.
If called with
.Dv CRYPTO_ALGORITHM_MAX + 1 ,
all algorithms registered for a driver will be unregistered in one go
and the driver will be disabled (no new sessions will be allocated on
that driver, and any existing sessions will be migrated to other
drivers).
The same will be done if all algorithms associated with a driver are
unregistered one by one.
.Pp
The calling convention for the three driver-supplied routines is:
.Bd -literal
int (*newsession) (u_int32_t *, struct cryptoini *);
int (*freesession) (u_int64_t);
int (*process) (struct cryptop *);
.Ed
.Pp
On invocation, the first argument to
.Fn newsession
contains the driver identifier obtained via
.Fn crypto_get_driverid .
On successfully returning, it should contain a driver-specific session
identifier.
The second argument is identical to that of
.Fn crypto_newsession .
.Pp
The
.Fn freesession
routine takes as argument the SID (which is the concatenation of the
driver identifier and the driver-specific session identifier).
It should clear any context associated with the session (clear hardware
registers, memory, etc.).
.Pp
The
.Fn process
routine is invoked with a request to perform crypto processing.
This routine must not block, but should queue the request and return
immediately.
Upon processing the request, the callback routine should be invoked.
In case of error, the error indication must be placed in the
.Fa crp_etype
field of the
.Fa cryptop
structure.
When the request is completed, or an error is detected, the
.Fn process
routine should invoke
.Fn crypto_done .
Session migration may be performed, as mentioned previously.
.Sh RETURN VALUES
.Fn crypto_register ,
.Fn crypto_unregister ,
.Fn crypto_newsession ,
and
.Fn crypto_freesession
return 0 on success, or an error code on failure.
.Fn crypto_get_driverid
returns a non-negative value on error, and \-1 on failure.
.Fn crypto_getreq
returns a pointer to a
.Fa cryptop
structure and
.Dv NULL
on failure.
.Fn crypto_dispatch
returns
.Er EINVAL
if its argument or the callback function was
.Dv NULL ,
and 0 otherwise.
The callback is provided with an error code in case of failure, in the
.Fa crp_etype
field.
.Sh FILES
.Bl -tag -width sys/crypto/crypto.c
.It Pa sys/crypto/crypto.c
most of the framework code
.El
.Sh SEE ALSO
.Xr ipsec 4 ,
.Xr pcmcia 4 ,
.Xr malloc 9 ,
.Xr tsleep 9
.Sh HISTORY
The cryptographic framework first appeared in
.Ox 2.7
and was written by
.An Angelos D. Keromytis Aq Mt angelos@openbsd.org .
.Sh BUGS
The framework currently assumes that all the algorithms in a
.Fn crypto_newsession
operation must be available by the same driver.
If that's not the case, session initialization will fail.
.Pp
The framework also needs a mechanism for determining which driver is
best for a specific set of algorithms associated with a session.
Some type of benchmarking is in order here.
.Pp
Multiple instances of the same algorithm in the same session are not
supported.
.Pp
A queue for completed operations should be implemented and processed
at some software
.Xr spl 9
level, to avoid overall system latency issues, and potential kernel
stack exhaustion while processing a callback.