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

From:  Linus Torvalds <>
To:  Vasiliy Kulikov <>
Subject:  Re: [RFC v1] implement SL*B and stack usercopy runtime checks
Date:  Sun, 3 Jul 2011 11:27:47 -0700
Message-ID:  <>
Cc:, Thomas Gleixner <>, Ingo Molnar <>, "H. Peter Anvin" <>,, Arnd Bergmann <>, Christoph Lameter <>, Pekka Enberg <>, Matt Mackall <>, Andrew Morton <>,,,
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.


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.


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