drivers/char/random.c: fix priming of last_data

Commit ec8f02da9ea5 ("random: prime last_data value per fips
requirements") added priming of last_data per fips requirements.

Unfortuantely, it did so in a way that can lead to multiple threads all
incrementing nbytes, but only one actually doing anything with the extra
data, which leads to some fun random corruption and panics.

The fix is to simply do everything needed to prime last_data in a single
shot, so there's no window for multiple cpus to increment nbytes -- in
fact, we won't even increment or decrement nbytes anymore, we'll just
extract the needed EXTRACT_SIZE one time per pool and then carry on with
the normal routine.

All these changes have been tested across multiple hosts and
architectures where panics were previously encoutered.  The code changes
are are strictly limited to areas only touched when when booted in fips
mode.

This change should also go into 3.8-stable, to make the myriads of fips
users on 3.8.x happy.

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Tested-by: Jan Stodola <jstodola@redhat.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Matt Mackall <mpm@selenic.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Blechd0se <alex.christ@hotmail.de>
random: fix accounting race condition with lockless irq entropy_count update

Commit 902c098a3663 ("random: use lockless techniques in the interrupt
path") turned IRQ path from being spinlock protected into lockless
cmpxchg-retry update.

That commit removed r->lock serialization between crediting entropy bits
from IRQ context and accounting when extracting entropy on userspace
read path, but didn't turn the r->entropy_count reads/updates in
account() to use cmpxchg as well.

It has been observed, that under certain circumstances this leads to
read() on /dev/urandom to return 0 (EOF), as r->entropy_count gets
corrupted and becomes negative, which in turn results in propagating 0
all the way from account() to the actual read() call.

Convert the accounting code to be the proper lockless counterpart of
what has been partially done by 902c098a3663.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Greg KH <greg@kroah.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Blechd0se <alex.christ@hotmail.de>
char: Convert use of typedef ctl_table to struct ctl_table

This typedef is unnecessary and should just be removed.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Blechd0se <alex.christ@hotmail.de>

Conflicts:
	drivers/char/random.c
random: run random_int_secret_init() run after all late_initcalls

The some platforms (e.g., ARM) initializes their clocks as
late_initcalls for some unknown reason.  So make sure
random_int_secret_init() is run after all of the late_initcalls are
run.

Cc: stable@vger.kernel.org
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Blechd0se <alex.christ@hotmail.de>

Conflicts:
	init/main.c
random: allow architectures to optionally define random_get_entropy()

Allow architectures which have a disabled get_cycles() function to
provide a random_get_entropy() function which provides a fine-grained,
rapidly changing counter that can be used by the /dev/random driver.

For example, an architecture might have a rapidly changing register
used to control random TLB cache eviction, or DRAM refresh that
doesn't meet the requirements of get_cycles(), but which is good
enough for the needs of the random driver.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Blechd0se <alex.christ@hotmail.de>
random: mix in architectural randomness earlier in extract_buf()

Previously if CPU chip had a built-in random number generator (i.e.,
RDRAND on newer x86 chips), we mixed it in at the very end of
extract_buf() using an XOR operation.

We now mix it in right after the calculate a hash across the entire
pool.  This has the advantage that any contribution of entropy from
the CPU's HWRNG will get mixed back into the pool.  In addition, it
means that if the HWRNG has any defects (either accidentally or
maliciously introduced), this will be mitigated via the non-linear
transform of the SHA-1 hash function before we hand out generated
output.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Blechd0se <alex.christ@hotmail.de>
random: statically compute poolbitshift, poolbytes, poolbits

Use a macro to statically compute poolbitshift (will be used in a
subsequent patch), poolbytes, and poolbits.  On virtually all
architectures the cost of a memory load with an offset is the same as
the one of a memory load.

It is still possible for this to generate worse code since the C
compiler doesn't know the fixed relationship between these fields, but
that is somewhat unlikely.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Blechd0se <alex.christ@hotmail.de>
random: allow fractional bits to be tracked

Allow fractional bits of entropy to be tracked by scaling the entropy
counter (fixed point).  This will be used in a subsequent patch that
accounts for entropy lost due to overwrites.

[ Modified by tytso to fix up a few missing places where the
  entropy_count wasn't properly converted from fractional bits to
  bits. ]

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Blechd0se <alex.christ@hotmail.de>
random: account for entropy loss due to overwrites

When we write entropy into a non-empty pool, we currently don't
account at all for the fact that we will probabilistically overwrite
some of the entropy in that pool.  This means that unless the pool is
fully empty, we are currently *guaranteed* to overestimate the amount
of entropy in the pool!

Assuming Shannon entropy with zero correlations we end up with an
exponentally decaying value of new entropy added:

	entropy <- entropy + (pool_size - entropy) *
		(1 - exp(-add_entropy/pool_size))

However, calculations involving fractional exponentials are not
practical in the kernel, so apply a piecewise linearization:

	  For add_entropy <= pool_size/2 then

	  (1 - exp(-add_entropy/pool_size)) >= (add_entropy/pool_size)*0.7869...

	  ... so we can approximate the exponential with
	  3/4*add_entropy/pool_size and still be on the
	  safe side by adding at most pool_size/2 at a time.

In order for the loop not to take arbitrary amounts of time if a bad
ioctl is received, terminate if we are within one bit of full.  This
way the loop is guaranteed to terminate after no more than
log2(poolsize) iterations, no matter what the input value is.  The
vast majority of the time the loop will be executed exactly once.

The piecewise linearization is very conservative, approaching 3/4 of
the usable input value for small inputs, however, our entropy
estimation is pretty weak at best, especially for small values; we
have no handle on correlation; and the Shannon entropy measure (Rényi
entropy of order 1) is not the correct one to use in the first place,
but rather the correct entropy measure is the min-entropy, the Rényi
entropy of infinite order.

As such, this conservatism seems more than justified.

This does introduce fractional bit values.  I have left it to have 3
bits of fraction, so that with a pool of 2^12 bits the multiply in
credit_entropy_bits() can still fit into an int, as 2*(3+12) < 31.  It
is definitely possible to allow for more fractional accounting, but
that multiply then would have to be turned into a 32*32 -> 64 multiply.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: DJ Johnston <dj.johnston@intel.com>
Signed-off-by: Blechd0se <alex.christ@hotmail.de>