148 lines
4.6 KiB
Groff
148 lines
4.6 KiB
Groff
.\" $NetBSD: rndsink.9,v 1.2 2013/06/24 04:21:20 riastradh Exp $
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.\"
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.\" Copyright (c) 2013 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This documentation is derived from text contributed to The NetBSD
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.\" Foundation by Taylor R. Campbell.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd April 10, 2013
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.Dt RNDSINK 9
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.Os
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.Sh NAME
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.Nm rndsink ,
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.Nm rndsink_create ,
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.Nm rndsink_destroy ,
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.Nm rndsink_request ,
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.Nm rndsink_schedule ,
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.Nd functions to asynchronously request entropy from the system entropy pool
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.Sh SYNOPSIS
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.In sys/rndsink.h
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.Ft struct rndsink *
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.Fn rndsink_create "size_t bytes" "void (*callback)(void *, const void *, size_t)" "void *arg"
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.Ft void
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.Fn rndsink_destroy "struct rndsink *rndsink"
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.Ft bool
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.Fn rndsink_request "struct rndsink *rndsink" "void *buffer" "size_t bytes"
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.Ft void
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.Fn rndsink_schedule "struct rndsink *rndsink"
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.Sh DESCRIPTION
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The
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.Nm
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functions support asynchronous requests for entropy from the system
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entropy pool.
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Users must call
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.Fn rndsink_create
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to create an rndsink which they may then pass to
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.Fn rndsink_request
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to request data from the system entropy pool.
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If full entropy is not available, the system will call a callback when
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entropy is next available.
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Users can schedule a callback without requesting data now using
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.Fn rndsink_schedule .
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When users no longer need an rndsink, they must pass it to
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.Fn rndsink_destroy .
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.Pp
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This API provides direct access to the system entropy pool.
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Most users should use the
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.Xr cprng 9
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API instead, which interposes a cryptographic pseudorandom number
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generator between the user and the entropy pool.
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.Sh FUNCTIONS
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.Bl -tag -width abcd
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.It Fn rndsink_create bytes callback arg
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Create an rndsink for requests of
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.Fa bytes
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bytes of entropy, which must be no more than
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.Dv RNDSINK_MAX_BYTES .
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When requested and enough entropy is available, the system will call
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.Fa callback
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with three arguments:
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.Bl -item -offset indent
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.It
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.Fa arg ,
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an arbitrary user-supplied pointer;
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.It
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a pointer to a buffer containing the bytes of entropy; and
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.It
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the number of bytes in the buffer, which will always be
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.Fa bytes .
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.El
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.Pp
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The callback will be called in soft interrupt context.
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.Pp
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.Fn rndsink_create
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may sleep to allocate memory.
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.It Fn rndsink_destroy rndsink
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Destroy an rndsink.
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.Fn rndsink_destroy
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may sleep to wait for pending callbacks to complete and to deallocate
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memory.
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.It Fn rndsink_request rndsink buffer bytes
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Store
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.Fa bytes
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bytes derived from the system entropy pool in
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.Fa buffer .
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If the bytes have full entropy, return true.
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Otherwise, schedule a callback as if with
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.Fn rndsink_schedule
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and return false.
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In either case,
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.Fn rndsink_request
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will store data in
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.Fa buffer .
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The argument
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.Fa bytes
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must be the same as the argument to
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.Fn rndsink_create
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that was used to create
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.Fa rndsink .
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May be called at
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.Dv IPL_VM
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or lower.
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The caller should use
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.Xr explicit_memset 3
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to clear
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.Fa buffer
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once it has used the data stored there.
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.It Fn rndsink_schedule rndsink
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Schedule a callback when the system entropy pool has enough entropy.
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If a callback is already scheduled, it remains scheduled.
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May be called at
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.Dv IPL_VM
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or lower.
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.El
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.Sh CODE REFERENCES
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The rndsink API is implemented in
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.Pa sys/kern/kern_rndsink.c
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and
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.Pa sys/sys/rndsink.h .
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.Sh SEE ALSO
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.Xr explicit_memset 3 ,
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.Xr cprng 9 ,
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.Xr rnd 9
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.Sh HISTORY
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The rndsink API first appeared in
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.Nx 7.0 .
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