[LLVMdev] Adding diversity for security (and testing)
criswell at illinois.edu
Tue Sep 10 08:19:53 PDT 2013
On 9/9/13 5:24 PM, Nick Lewycky wrote:
> Briefly looking at ASAN again, I saw a performance penalty of 2x
> mentioned. Diversity could act as both defense in depth, and as a
> lower-impact defense for performance critical code.
> Okay, I've been thinking about what I wanted answered here, and I've
> decided that what I want to know is too complex for this discussion.
> It boils down to: given we have all the power of clang and llvm for
> very complex analysis, both static and dynamic, why is randomizing the
> best we can do? Can't we somehow use all that static and dynamic
> analysis to shrink the problem down to something we can solve more
> cleverly than randomizing the program across a lot of axes, such as
> proving (or arranging for) certain properties which reduce how much we
> need to randomize, etc? And if not *why can't we*? It's that last part
> which I think is hardest to answer, so I've decided I'll leave this to
> the security-trained folks -- if they think this is the right
> approach, they're probably right.
You are right that, with LLVM and Clang's facilities, we can do better.
However, in my opinion, the cost of many of these solutions is still too
high (both in terms of development cost and run-time performance) for
industry to accept them. I am also of the opinion that many people do
not understand the options that are available, partially because the
work on the subject is spread across 4 different communities (compiler,
operating systems, security, and software engineering).
Automatic, very strong memory safety guarantees are hard to enforce on
existing C code with good efficiency. It can be done, but it requires
sophisticated analyses (e.g., type-inferencing, whole-program points-to
analysis) and, therefore, requires a decent level of expertise and
incurs significant developer cost. Industry is also very picky about
run-time performance; Vikram and I were told once by a bay-area company
that they would only use a security solution if it added 0% run-time
overhead. Such performance goals will kill just about any solution.
Enforcing a weaker property like control-flow integrity looks very
promising both in terms of development cost, performance overhead, and
security. I'm not sure why it doesn't get more attention. Perhaps no
one is yet willing to work out the remaining compatibility issues with
native code libraries, or maybe industry wants someone else to build an
open-source implementation first before committing to further
development, or maybe people simply are unaware of what it is. I'm
curious to know.
If you're interested in knowing more about the topic, take a look at the
Memory Safety Menagerie at http://sva.cs.illinois.edu/menagerie. I need
to update it since a few new papers have come out, but it provides a
good number of papers on the subject (including quite a few that use LLVM).
My two cents.
-- John T.
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