i2c-aspeed testing with kunit fake and syzkaller

Brendan Higgins brendanhiggins at google.com
Wed Oct 9 11:00:36 AEDT 2019

+kunit-dev at googlegroups.com

On Tue, Oct 8, 2019 at 7:44 AM Dmitry Vyukov <dvyukov at google.com> wrote:
> 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

The mock_do_expect thing is definitely an issue, but also, not
upstream, so I will fix it before I send that out for review.

As for aspeed_i2c_master_xfer(); the issue appears to be that we do a
wait_for_completion_timeout, which should be interruptible. So I
should probably submit a fix for that.

I was less confident in i2c_transfer, i2c_smbus_xfer, and
__of_find_property; nevertheless:

i2c_transfer doesn't actually look like a bug. It looks like the
faking framework aborted, resulting in a condition which can never
happen in the i2c-core in the real world. Same goes for

The issue in __of_find_property appears to be that it hits a property
which was not properly initialized when the device_node was
initialized with of_node_init()[1]. I am not an expert in how the
device tree stuff works, but I would expect that of_node_init() should
fully initialize the device_node passed to it. So that might be a
legitimate issue.

I'll take a closer look at i2c_transfer, and i2c_smbus_xfer and see if
I missed anything.


More information about the Linux-aspeed mailing list