This is a note to let you know that I've just added the patch titled
crypto: jitter - consider 32 LSB for APT
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
crypto-jitter-consider-32-lsb-for-apt.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit f6dd293acffab3f64e634192c2c7588b296ca4f0
Author: Stephan Müller <smueller@xxxxxxxxxx>
Date: Sun Nov 21 15:14:20 2021 +0100
crypto: jitter - consider 32 LSB for APT
[ Upstream commit 552d03a223eda3df84526ab2c1f4d82e15eaee7a ]
The APT compares the current time stamp with a pre-set value. The
current code only considered the 4 LSB only. Yet, after reviews by
mathematicians of the user space Jitter RNG version >= 3.1.0, it was
concluded that the APT can be calculated on the 32 LSB of the time
delta. Thi change is applied to the kernel.
This fixes a bug where an AMD EPYC fails this test as its RDTSC value
contains zeros in the LSB. The most appropriate fix would have been to
apply a GCD calculation and divide the time stamp by the GCD. Yet, this
is a significant code change that will be considered for a future
update. Note, tests showed that constantly the GCD always was 32 on
these systems, i.e. the 5 LSB were always zero (thus failing the APT
since it only considered the 4 LSB for its calculation).
Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c
index 6e147c43fc186..37c4c308339e4 100644
--- a/crypto/jitterentropy.c
+++ b/crypto/jitterentropy.c
@@ -265,7 +265,6 @@ static int jent_stuck(struct rand_data *ec, __u64 current_delta)
{
__u64 delta2 = jent_delta(ec->last_delta, current_delta);
__u64 delta3 = jent_delta(ec->last_delta2, delta2);
- unsigned int delta_masked = current_delta & JENT_APT_WORD_MASK;
ec->last_delta = current_delta;
ec->last_delta2 = delta2;
@@ -274,7 +273,7 @@ static int jent_stuck(struct rand_data *ec, __u64 current_delta)
* Insert the result of the comparison of two back-to-back time
* deltas.
*/
- jent_apt_insert(ec, delta_masked);
+ jent_apt_insert(ec, current_delta);
if (!current_delta || !delta2 || !delta3) {
/* RCT with a stuck bit */
