** Changed in: linux-aws (Ubuntu Focal)
Assignee: (unassigned) => Andrea Righi (arighi)
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https://bugs.launchpad.net/bugs/1927692
Title:
AWS: out of entropy on Graviton 2 instances types (mg6.*)
Status in linux-aws package in Ubuntu:
Fix Released
Status in linux-aws source package in Focal:
In Progress
Bug description:
[Impact]
AWS Graviton 2 instances do not have enough entropy available at boot,
so any task that require entropy (even reading few bytes from
/dev/random) will be stuck forever.
[Fix]
The proper fix for this problem is to correctly refill the entropy
pool with some real random data using some hardware-generated
randomness.
In the meantime a reasonable workaround can be to apply the following
upstream commits:
30c08efec888 random: make /dev/random be almost like /dev/urandom
48446f198f9a random: ignore GRND_RANDOM in getentropy(2)
75551dbf112c random: add GRND_INSECURE to return best-effort
non-cryptographic bytes
c6f1deb15878 random: Add a urandom_read_nowait() for random APIs that don't
warn
4c8d062186d9 random: Don't wake crng_init_wait when crng_init == 1
In this way the system will not run out of entropy and will be able to
provide best-effort randomness in any case, preventing the out of entropy issue
on the AWS Gravion 2 instances.
[Test plan]
Execute the following command on any m6g instance:
dd bs=32 count=1 if=/dev/random of=/dev/null
This should return quickly, if not it means that the system does not
have enough entropy available. When the problem happens this command
hangs forever.
[Where problems could occur]
This changes affect the read semantics of /dev/random to be the same
as /dev/urandom except that reads will block until the CRNG is ready.
This should not materially break any API. Any code that worked without
these changes should work at least as well as before. However,
applications that have strict randomness requirements might be
affected by the provided best-effort randomness, so we may need to
apply more commits/changes to introduce a proper hardware entropy
support on Graviton 2 instances to provide a better quality of
randomness. In the meantime these upstream changes consist a
reasonable workaround to prevent applications from hanging forever on
the mg6.* instances.
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