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Re: [RFC v1] implement SL*B and stack usercopy runtime checks

From:  Linus Torvalds <torvalds-AT-linux-foundation.org>
To:  Vasiliy Kulikov <segoon-AT-openwall.com>
Subject:  Re: [RFC v1] implement SL*B and stack usercopy runtime checks
Date:  Sun, 3 Jul 2011 11:27:47 -0700
Message-ID:  <CA+55aFzXEoTyK0Sm-y=6xGmLMWzQiSQ7ELJ2-WL_PrP3r44MSg@mail.gmail.com>
Cc:  kernel-hardening-AT-lists.openwall.com, Thomas Gleixner <tglx-AT-linutronix.de>, Ingo Molnar <mingo-AT-redhat.com>, "H. Peter Anvin" <hpa-AT-zytor.com>, x86-AT-kernel.org, Arnd Bergmann <arnd-AT-arndb.de>, Christoph Lameter <cl-AT-linux-foundation.org>, Pekka Enberg <penberg-AT-kernel.org>, Matt Mackall <mpm-AT-selenic.com>, Andrew Morton <akpm-AT-linux-foundation.org>, linux-kernel-AT-vger.kernel.org, linux-arch-AT-vger.kernel.org, linux-mm-AT-kvack.org
Archive-link:  Article

That patch is entirely insane. No way in hell will that ever get merged.

copy_to/from_user() is some of the most performance-critical code, and
runs a *lot*, often for fairly small structures (ie 'fstat()' etc).

Adding random ad-hoc tests to it is entirely inappropriate. Doing so
unconditionally is insane.

So NAK, NAK, NAK.

If you seriously clean it up (that at a minimum includes things like
making it configurable using some pretty helper function that just
compiles away for all the normal cases, and not writing out

   if (!slab_access_ok(to, n) || !stack_access_ok(to, n))

multiple times, for chrissake) it _might_ be acceptable.

But in its current form it's just total crap. It's exactly the kind of
"crazy security people who don't care about anything BUT security"
crap that I refuse to see.

Some balance and sanity.

                      Linus

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