On Thu, Mar 10, 2022 at 06:24:59PM -0500, Brian Masney wrote: > The generate function in struct rng_alg expects that the destination > buffer is completely filled if the function returns 0. qcom_rng_read() > can run into a situation where the buffer is partially filled with > randomness and the remaining part of the buffer is zeroed since > qcom_rng_generate() doesn't check the return value. This issue can > be reproduced by running the following from libkcapi: > > kcapi-rng -b 9000000 > OUTFILE > > The generated OUTFILE will have three huge sections that contain all > zeros, and this is caused by the code where the test > 'val & PRNG_STATUS_DATA_AVAIL' fails. > > Let's fix this issue by ensuring that qcom_rng_read() always returns > with a full buffer if the function returns success. Let's also have > qcom_rng_generate() return the correct value. > > Here's some statistics from the ent project > (https://www.fourmilab.ch/random/) that shows information about the > quality of the generated numbers: > > $ ent -c qcom-random-before > Value Char Occurrences Fraction > 0 606748 0.067416 > 1 33104 0.003678 > 2 33001 0.003667 > ... > 253 � 32883 0.003654 > 254 � 33035 0.003671 > 255 � 33239 0.003693 > > Total: 9000000 1.000000 > > Entropy = 7.811590 bits per byte. > > Optimum compression would reduce the size > of this 9000000 byte file by 2 percent. > > Chi square distribution for 9000000 samples is 9329962.81, and > randomly would exceed this value less than 0.01 percent of the > times. > > Arithmetic mean value of data bytes is 119.3731 (127.5 = random). > Monte Carlo value for Pi is 3.197293333 (error 1.77 percent). > Serial correlation coefficient is 0.159130 (totally uncorrelated = > 0.0). > > Without this patch, the results of the chi-square test is 0.01%, and > the numbers are certainly not random according to ent's project page. > The results improve with this patch: > > $ ent -c qcom-random-after > Value Char Occurrences Fraction > 0 35432 0.003937 > 1 35127 0.003903 > 2 35424 0.003936 > ... > 253 � 35201 0.003911 > 254 � 34835 0.003871 > 255 � 35368 0.003930 > > Total: 9000000 1.000000 > > Entropy = 7.999979 bits per byte. > > Optimum compression would reduce the size > of this 9000000 byte file by 0 percent. > > Chi square distribution for 9000000 samples is 258.77, and randomly > would exceed this value 42.24 percent of the times. > > Arithmetic mean value of data bytes is 127.5006 (127.5 = random). > Monte Carlo value for Pi is 3.141277333 (error 0.01 percent). > Serial correlation coefficient is 0.000468 (totally uncorrelated = > 0.0). > > This change was tested on a Nexus 5 phone (msm8974 SoC). > > Signed-off-by: Brian Masney <bmasney@xxxxxxxxxx> > Fixes: ceec5f5b5988 ("crypto: qcom-rng - Add Qcom prng driver") > Cc: stable@xxxxxxxxxxxxxxx # 4.19+ > --- > drivers/crypto/qcom-rng.c | 17 ++++++++++------- > 1 file changed, 10 insertions(+), 7 deletions(-) Patch applied. Thanks. -- Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
