Re: [PATCH v4] mm, kasan: switch SLUB to stackdepot, enable memory quarantine for SLUB

On Mon, Jun 20, 2016 at 9:50 PM, Sasha Levin [off-list ref] wrote:

On 06/20/2016 08:53 AM, Alexander Potapenko wrote:

quoted

On Sun, Jun 19, 2016 at 7:40 PM, Sasha Levin [off-list ref] wrote:

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On 06/19/2016 03:24 AM, Alexander Potapenko wrote:

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Hi Sasha,

This commit delays the reuse of memory after it has been freed, so
it's intended to help people find more use-after-free errors.

Is there a way to tell if the use-after-free access was to a memory
that is quarantined?

quoted

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But I'm puzzled why the stacks are missing.

I looked at the logs, it looks like stackdepot ran out of room pretty
early during boot.

This is quite strange, as there's room for ~80k stacks in the depot,
and usually the number of unique stacks is lower than 30k.
I wonder if this is specific to your config, can you please share it
(assuming you're using ToT kernel)?
Attached is the patch that you can try out to dump the new stacks
after 30k - it's really interesting where do they come from (note the
patch is not for submission).

Attached a log file generated with that patch, and my kernel config.

I haven't looked close yet, but your log contains 1455 unique
'DRIVERNAME_driver_init' function names, for which it's quite likely
that 80k allocation stacks are generated.
Can you remove the dump_stack() call from my patch, fuzz for a while
and see to which number does |alloc_cnt| converge on your machine?
Maybe our estimate was just too optimistic, and we need to increase
the memory limit for the stack depot.

Thanks,
Sasha

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Alexander Potapenko
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