Re: [PATCH v14 0/6] Introduce the STACKLEAK feature and a test for it

[Ingo Molnar <mingo@kernel.org>]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Wed, Jul 11, 2018 at 1:37 PM Alexander Popov <alex.popov@linux.com> wrote:
> >
> > This is the 14th version of the patch series introducing STACKLEAK
> > to the mainline kernel for x86. This version comes with style changes
> > according to the feedback from Ingo Molnar and includes Laura Abbott's
> > modifications of scripts/Makefile.gcc-plugins.
> 
> As before, I will repeat that I think 1% on a kernel compile (which
> has almost no actual kernel footprint) is a huge cost, and other -
> more kernel-centric - loads will likely see much worse performance.
> 
> And I still think that this is stupid, and peoples time would be
> *much* better spent on plugins that have much lower costs and get
> pretty much the same advanytages (ie the whole "just initialize all
> automatics to zero" thing or similar).
> 
> But whatever. I'll just continue to tell people not to use silly
> config options that have a high cost-to-point ratio. If people *want*
> to waste their CPU, that's their problem.

So I agree that it's pretty stupid. Since 95%+ of our users just use what the 
distro configured - so at minimum I'd like to see a runtime patching based way
for root to disable it, so that people (who care or who are hurt by it) can
turn the check off - which should be the most expensive part causing much of the 1% 
overhead.

Shouldn't be too hard to implement, this is just a checking method called for 
every system call that does nothing substantial in 99.99999% of the cases.

Thanks,

	Ingo