Pull /dev/random changes from Ted Ts'o:
"The /dev/random changes for 3.13 including a number of improvements in
the following areas: performance, avoiding waste of entropy, better
tracking of entropy estimates, support for non-x86 platforms that have
a register which can't be used for fine-grained timekeeping, but which
might be good enough for the random driver.
Also add some printk's so that we can see how quickly /dev/urandom can
get initialized, and when programs try to use /dev/urandom before it
is fully initialized (since this could be a security issue). This
shouldn't be an issue on x86 desktop/laptops --- a test on my Lenovo
T430s laptop shows that /dev/urandom is getting fully initialized
approximately two seconds before the root file system is mounted
read/write --- this may be an issue with ARM and MIPS embedded/mobile
systems, though. These printk's will be a useful canary before
potentially adding a future change to start blocking processes which
try to read from /dev/urandom before it is initialized, which is
something FreeBSD does already for security reasons, and which
security folks have been agitating for Linux to also adopt"
* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
random: add debugging code to detect early use of get_random_bytes()
random: initialize the last_time field in struct timer_rand_state
random: don't zap entropy count in rand_initialize()
random: printk notifications for urandom pool initialization
random: make add_timer_randomness() fill the nonblocking pool first
random: convert DEBUG_ENT to tracepoints
random: push extra entropy to the output pools
random: drop trickle mode
random: adjust the generator polynomials in the mixing function slightly
random: speed up the fast_mix function by a factor of four
random: cap the rate which the /dev/urandom pool gets reseeded
random: optimize the entropy_store structure
random: optimize spinlock use in add_device_randomness()
random: fix the tracepoint for get_random_bytes(_arch)
random: account for entropy loss due to overwrites
random: allow fractional bits to be tracked
random: statically compute poolbitshift, poolbytes, poolbits
random: mix in architectural randomness earlier in extract_buf()
The Tausworthe PRNG is initialized at late_initcall time. At that time the
entropy pool serving get_random_bytes is not filled sufficiently. This
patch adds an additional reseeding step as soon as the nonblocking pool
gets marked as initialized.
On some machines it might be possible that late_initcall gets called after
the pool has been initialized. In this situation we won't reseed again.
(A call to prandom_seed_late blocks later invocations of early reseed
attempts.)
Joint work with Daniel Borkmann.
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Since we initialize jiffies to wrap five minutes before boot (see
INITIAL_JIFFIES defined in include/linux/jiffies.h) it's important to
make sure the last_time field is initialized to INITIAL_JIFFIES.
Otherwise, the entropy estimator will overestimate the amount of
entropy resulting from the first call to add_timer_randomness(),
generally by about 8 bits.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
The rand_initialize() function was being run fairly late in the kernel
boot sequence. This was unfortunate, since it zero'ed the entropy
counters, thus throwing away credit that was accumulated earlier in
the boot sequence, and it also meant that initcall functions run
before rand_initialize were using a minimally initialized pool.
To fix this, fix init_std_data() to no longer zap the entropy counter;
it wasn't necessary, and move rand_initialize() to be an early
initcall.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Print a notification to the console when the nonblocking pool is
initialized. Also printk a warning when a process tries reading from
/dev/urandom before it is fully initialized.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Change add_timer_randomness() so that it directs incoming entropy to
the nonblocking pool first if it hasn't been fully initialized yet.
This matches the strategy we use in add_interrupt_randomness(), which
allows us to push the randomness where we need it the most during when
the system is first booting up, so that get_random_bytes() and
/dev/urandom become safe to use as soon as possible.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Pull /dev/random changes from Ted Ts'o:
"These patches are designed to enable improvements to /dev/random for
non-x86 platforms, in particular MIPS and ARM"
* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
random: allow architectures to optionally define random_get_entropy()
random: run random_int_secret_init() run after all late_initcalls
Instead of using the random driver's ad-hoc DEBUG_ENT() mechanism, use
tracepoints instead. This allows for a much more fine-grained control
of which debugging mechanism which a developer might need, and unifies
the debugging messages with all of the existing tracepoints.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
As the input pool gets filled, start transfering entropy to the output
pools until they get filled. This allows us to use the output pools
to store more system entropy. Waste not, want not....
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
The add_timer_randomness() used to drop into trickle mode when entropy
pool was estimated to be 87.5% full. This was important when
add_timer_randomness() was used to sample interrupts. It's not used
for this any more --- add_interrupt_randomness() now uses fast_mix()
instead. By elimitating trickle mode, it allows us to fully utilize
entropy provided by add_input_randomness() and add_disk_randomness()
even when the input pool is above the old trickle threshold of 87.5%.
This helps to answer the criticism in [1] in their hypothetical
scenario where our entropy estimator was inaccurate, even though the
measurements in [2] seem to indicate that our entropy estimator given
real-life entropy collection is actually pretty good, albeit on the
conservative side (which was as it was designed).
[1] http://eprint.iacr.org/2013/338.pdf
[2] http://eprint.iacr.org/2012/251.pdf
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Our mixing functions were analyzed by Lacharme, Roeck, Strubel, and
Videau in their paper, "The Linux Pseudorandom Number Generator
Revisited" (see: http://eprint.iacr.org/2012/251.pdf).
They suggested a slight change to improve our mixing functions
slightly. I also adjusted the comments to better explain what is
going on, and to document why the polynomials were changed.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
By mixing the entropy in chunks of 32-bit words instead of byte by
byte, we can speed up the fast_mix function significantly. Since it
is called on every single interrupt, on systems with a very heavy
interrupt load, this can make a noticeable difference.
Also fix a compilation warning in add_interrupt_randomness() and avoid
xor'ing cycles and jiffies together just in case we have an
architecture which tries to define random_get_entropy() by returning
jiffies.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reported-by: Jörn Engel <joern@logfs.org>
In order to avoid draining the input pool of its entropy at too high
of a rate, enforce a minimum time interval between reseedings of the
urandom pool. This is set to 60 seconds by default.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
The add_device_randomness() function calls mix_pool_bytes() twice for
the input pool and the non-blocking pool, for a total of four times.
By using _mix_pool_byte() and taking the spinlock in
add_device_randomness(), we can halve the number of times we need
take each pool's spinlock.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Fix a problem where get_random_bytes_arch() was calling the tracepoint
get_random_bytes(). So add a new tracepoint for
get_random_bytes_arch(), and make get_random_bytes() and
get_random_bytes_arch() call their correct tracepoint.
Also, add a new tracepoint for add_device_randomness()
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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>
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>
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>
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>
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
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>
After the last architecture switched to generic hard irqs the config
options HAVE_GENERIC_HARDIRQS & GENERIC_HARDIRQS and the related code
for !CONFIG_GENERIC_HARDIRQS can be removed.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
