i2c-aspeed testing with kunit fake and syzkaller

[Dmitry Vyukov]

Hi i2c/aspeed-related people,

Some time ago Brendan and myself did an experiment of testing the
i2c-aspeed driver in a qemu VM (without any hardware/emulation) using
kunit-based fake hardware. The fake allowed us to get 10 i2c devices
successfully probe and appear in /dev/. Which in turn allowed us to
test the actual driver with syzkaller.
I will just leave here some details and traces as FYI and for future
reference. I think this is an important precedent in general.

The kernel branch is here:
https://github.com/dvyukov/linux/commits/kunit-i2c-stub2
This is one of kunit branches with this commit on top:
https://github.com/dvyukov/linux/commit/c9c1706611fdc49679c5bf5bff1e147ab7c7aa79
This contains lots of hacks to get the fake working on x86 and leave
persistent devices initialized (rather than shutdown them after
unit-testing).

This is the kernel config:
https://gist.githubusercontent.com/dvyukov/72a31dad43b5687e6ffdcdb4cb342175/raw/24b706326e2d9202789fece5bfc17355aadda411/gistfile1.txt
(some i2c configs + a bunch of debugging configs).

If you boot this kernel with the config in qemu, you should see /dev/i2c-{0,10}.

Probably any syzkaller commit will work, but I just testing on this one:
https://github.com/google/syzkaller/tree/2ab6c4a4571d4170b0009a5b14b9789b016814b6
Here is syzkaller config I used:
https://gist.githubusercontent.com/dvyukov/d0a3c0e9b44cc7d445b36a8a50404ed8/raw/5f6aab34c6515cc4e96dac6cf3a98aaaf5e21b58/gistfile1.txt

Here is kernel coverage we achieved as the result of fuzzing:
https://drive.google.com/file/d/1JdNshmCWI3crJ3BuVo6uvRuHMBrwH5eB/view?usp=sharing

For crashes, I've got 3 different task hangs:

INFO: task hung in i2c_transfer
https://gist.githubusercontent.com/dvyukov/25e98a59b643bc868c7489f566ed9eab/raw/67b717488ae9af381a5b0615e5ddf2d226369d3c/gistfile1.txt

INFO: task hung in i2c_smbus_xfer
https://gist.githubusercontent.com/dvyukov/7ca87fea1b397d46e3393227a34595b9/raw/f5385f025abfc3ad2e91fd4f2616e58c7de8804e/gistfile1.txt

INFO: task hung in aspeed_i2c_master_xfer
https://gist.githubusercontent.com/dvyukov/dbc51e3ea7034f255c8fd1c99965d91a/raw/a5165e4e6c3b41d593d02fc22996104e468cfab3/gistfile1.txt

And some memory corruptions (non-thread-safe kunit data structures?):

KASAN: use-after-free Read in aspeed_i2c_fake_write_command_reg
https://gist.githubusercontent.com/dvyukov/6ca5bca5cf7a40a93636360635a4672c/raw/5ad0e7b33907f4b0db102b74c2a11237df612462/gistfile1.txt

KASAN: use-after-free Read in __of_find_property
https://gist.githubusercontent.com/dvyukov/95ed93a39d38fd215c141b58e5d3ec0f/raw/ea7f2346982a31ab16fca2850f91e1ef11faf687/gistfile1.txt

general protection fault in mock_do_expect
https://gist.githubusercontent.com/dvyukov/8c2e3def6775d39cb7496b56a77cbcd8/raw/5778337009e21397b484aafe5b24c87ebe64b63f/gistfile1.txt

There are probably a number of things that can be improved in kunit
platform mock, the fake driver and syzkaller i2c coverage, but this is
a starting point.

Thanks