linux-kernel - Re: [PATCH v1 1/1] lkdtm/stackleak: Make the stack erasing test more verbose

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Date:   Tue, 31 Dec 2019 01:20:24 +0300
From:   Alexander Popov <alex.popov@...ux.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, notify@...nel.org
Subject: Re: [PATCH v1 1/1] lkdtm/stackleak: Make the stack erasing test more
 verbose

Hello Kees!

On 30.12.2019 21:37, Kees Cook wrote:
> On Thu, Dec 19, 2019 at 05:54:16PM +0300, Alexander Popov wrote:
>> Make the stack erasing test more verbose about the errors that it
>> can detect. BUG() in case of test failure is useful when the test
>> is running in a loop.
> 
> Hi! I try to keep the "success" conditions for LKDTM tests to be a
> system exception, so doing "BUG" on a failure is actually against the
> design. So, really, a test harness needs to know to check dmesg for the
> results here. It almost looks like this check shouldn't live in LKDTM,

Hm, I see...

Let me explain why I've decided to use BUG() in case of a failure.

Once upon a time I noticed that the stack erasing test failed on a kernel with
KASAN enabled. It happened only once, and all my numerous efforts to reproduce
it failed. That's why I come with this patch. These changes provide additional
information and allow easy detection of a failure when you run the test in a loop.

Is stackleak test the only exception of this kind in LKDTM?

> but since it feels like other LKDTM tests, I'm happy to keep it there
> for now.

Do you mean that you will apply this patch?

> I'll resend my selftests series that adds a real test harness for all
> the LKDTM tests and CC you.

Ok!

Maybe you also see how to improve the LKDTM infrastructure and remove this
inconsistency. Could you share your ideas?

Best regards,
Alexander