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hw_random doc updates

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Update documentation for the hw_random support to be current:

 - Documentation/hw_random.txt has been updated to reflect the
   current code:  it's a framework now, a "core" with a small
   sysfs interface, that hardware-specific drivers plug in to.
   Text specific to Intel hardware is now at the end.

 - Kconfig now references the Documentation/hw_random.txt file
   and better explains what this really does.

Both chunks of documentation now higlight the fact that the kernel entropy
pool is maintained by "rngd", and this driver has nothing directly to do with
that important task.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Brownell 2008-03-24 12:29:51 -07:00 committed by Linus Torvalds
parent cb622bbb69
commit 537878d2c9
2 changed files with 50 additions and 22 deletions
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63
Documentation/hw_random.txt
View file

@ -1,20 +1,54 @@
Hardware driver for Intel/AMD/VIA Random Number Generators (RNG)
Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>
Introduction:
The hw_random device driver is software that makes use of a
The hw_random framework is software that makes use of a
special hardware feature on your CPU or motherboard,
a Random Number Generator (RNG).
a Random Number Generator (RNG). The software has two parts:
a core providing the /dev/hw_random character device and its
sysfs support, plus a hardware-specific driver that plugs
into that core.
In order to make effective use of this device driver, you
To make the most effective use of these mechanisms, you
should download the support software as well. Download the
latest version of the "rng-tools" package from the
hw_random driver's official Web site:
http://sourceforge.net/projects/gkernel/
Those tools use /dev/hw_random to fill the kernel entropy pool,
which is used internally and exported by the /dev/urandom and
/dev/random special files.
Theory of operation:
CHARACTER DEVICE. Using the standard open()
and read() system calls, you can read random data from
the hardware RNG device. This data is NOT CHECKED by any
fitness tests, and could potentially be bogus (if the
hardware is faulty or has been tampered with). Data is only
output if the hardware "has-data" flag is set, but nevertheless
a security-conscious person would run fitness tests on the
data before assuming it is truly random.
The rng-tools package uses such tests in "rngd", and lets you
run them by hand with a "rngtest" utility.
/dev/hw_random is char device major 10, minor 183.
CLASS DEVICE. There is a /sys/class/misc/hw_random node with
two unique attributes, "rng_available" and "rng_current". The
"rng_available" attribute lists the hardware-specific drivers
available, while "rng_current" lists the one which is currently
connected to /dev/hw_random. If your system has more than one
RNG available, you may change the one used by writing a name from
the list in "rng_available" into "rng_current".
==========================================================================
Hardware driver for Intel/AMD/VIA Random Number Generators (RNG)
Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>
About the Intel RNG hardware, from the firmware hub datasheet:
The Firmware Hub integrates a Random Number Generator (RNG)
@ -25,20 +59,7 @@ About the Intel RNG hardware, from the firmware hub datasheet:
access to our RNG for use as a security feature. At this time,
the RNG is only to be used with a system in an OS-present state.
Theory of operation:
Character driver. Using the standard open()
and read() system calls, you can read random data from
the hardware RNG device. This data is NOT CHECKED by any
fitness tests, and could potentially be bogus (if the
hardware is faulty or has been tampered with). Data is only
output if the hardware "has-data" flag is set, but nevertheless
a security-conscious person would run fitness tests on the
data before assuming it is truly random.
/dev/hwrandom is char device major 10, minor 183.
Driver notes:
Intel RNG Driver notes:
* FIXME: support poll(2)

9
drivers/char/hw_random/Kconfig
View file

@ -9,7 +9,14 @@ config HW_RANDOM
Hardware Random Number Generator Core infrastructure.
To compile this driver as a module, choose M here: the
module will be called rng-core.
module will be called rng-core. This provides a device
that's usually called /dev/hw_random, and which exposes one
of possibly several hardware random number generators.
These hardware random number generators do not feed directly
into the kernel's random number generator. That is usually
handled by the "rngd" daemon. Documentation/hw_random.txt
has more information.
If unsure, say Y.