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Date: Tue, 23 Oct 2018 12:30:44 -0700
From: Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [RFC PATCH 0/2] improve vmalloc allocation
Message-ID: <20181023193044.GA139403@joelaf.mtv.corp.google.com>
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To: Shuah Khan <shuah@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>, Matthew Wilcox <willy@infradead.org>, Uladzislau Rezki <urezki@gmail.com>, Kees Cook <keescook@chromium.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>, Thomas Garnier <thgarnie@google.com>, Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>, Steven Rostedt <rostedt@goodmis.org>, Joel Fernandes <joelaf@google.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>, Tejun Heo <tj@kernel.org>, maco@android.com

On Tue, Oct 23, 2018 at 11:13:36AM -0600, Shuah Khan wrote:
> On 10/23/2018 11:05 AM, Michal Hocko wrote:
> > On Tue 23-10-18 08:26:40, Matthew Wilcox wrote:
> >> On Tue, Oct 23, 2018 at 09:02:56AM -0600, Shuah Khan wrote:
> > [...]
> >>> The way it can be handled is by adding a test module under lib. test_kmod,
> >>> test_sysctl, test_user_copy etc.
> >>
> >> The problem is that said module can only invoke functions which are
> >> exported using EXPORT_SYMBOL.  And there's a cost to exporting them,
> >> which I don't think we're willing to pay, purely to get test coverage.
> > 
> > Yes, I think we do not want to export internal functionality which might
> > be still interesting for the testing coverage. Maybe we want something
> > like EXPORT_SYMBOL_KSELFTEST which would allow to link within the
> > kselftest machinery but it wouldn't allow the same for general modules
> > and will not give any API promisses.
> > 
> 
> I like this proposal. I think we will open up lot of test opportunities with
> this approach.
> 
> Maybe we can use this stress test as a pilot and see where it takes us.

I am a bit worried that such an EXPORT_SYMBOL_KSELFTEST mechanism can be abused by
out-of-tree module writers to call internal functionality.

How would you prevent that?

thanks,

 - Joel