Tag Archives: science

MalConv: Lessons learned from Deep Learning on executables

I don't usually write up my technical work here, mostly because I spend enough hours as is doing technical writing. But a co-author, Jon Barker, recently wrote a post on the NVIDIA Parallel For All blog about one of our papers on neural networks for detecting malware, so I thought I'd link to it here. (You can read the paper itself, "Malware Detection by Eating a Whole EXE" here.) Plus it was on the front page of Hacker News earlier this week, which is not something I thought would ever happen to my work.

Rather than rehashing everything in Jon's Parallel for All post about our work, I want to highlight some of the lessons we learned from doing this about ML/neural nets/deep learning.

As way of background, I'll lift a few paragraphs from Jon's introduction:

The paper introduces an artificial neural network trained to differentiate between benign and malicious Windows executable files with only the raw byte sequence of the executable as input. This approach has several practical advantages:

  • No hand-crafted features or knowledge of the compiler used are required. This means the trained model is generalizable and robust to natural variations in malware.
  • The computational complexity is linearly dependent on the sequence length (binary size), which means inference is fast and scalable to very large files.
  • Important sub-regions of the binary can be identified for forensic analysis.
  • This approach is also adaptable to new file formats, compilers and instruction set architectures—all we need is training data.

We also hope this paper demonstrates that malware detection from raw byte sequences has unique and challenging properties that make it a fruitful research area for the larger machine learning community.

One of the big issues we were confronting with our approach, MalConv, is that executables are often millions of bytes in length. That's orders of magnitude more time steps than most sequence processing networks deal with. Big data usually refers to lots and lots of small data points, but for us each individual sample was big. Saying this was a non-trivial problem is a serious understatement.

The MalConv architecture
Architecture of the malware detection network. (Image copyright NVIDIA.)

Here are three lessons we learned, not about malware or cybersecurity, but about the process of building neural networks on such unusual data.

1. Deep learning != image processing

The large majority of the work in deep learning has been done in the image domain. Of the remainder, the large majority has been in either text or speech. Many of the lessons, best practices, rules of thumb, etc., that we think apply to deep learning may actually be specific to these domains.

For instance, the community has settled around narrow convolutional filters, stacked with a lot of depth as being generally the best way to go. And for images, narrow-and-deep absolutely seems to be the correct choice. But in order to get a network that processes two million time steps to fit in memory at all (on beefy 16GB cards no less) we were forced to go wide-and-shallow.

With images, a pixel values is always a pixel value. 0x20 in a grayscale image is always darkish gray, no matter what. In an executable, a byte values are ridiculously polysemous: 0x20 may be part of an instruction, a string, a bit array, a compressed or encrypted values, an address, etc. You can't interpolate between values at all, so you can't resize or crop the way you would with images to make your data set smaller or introduce data augmentation. Binaries also play havoc with locality, since you can re-arrange functions in any order, among other things. You can't rely on any Tobbler's Law1 relationship the way you can in images, text, or speech.

2. BatchNorm isn't pixie dust

Batch Normalization has this bippity-boppity-boo magic quality. Just sprinkle it on top of your network architecture, and things that didn't converge before now do, and things that did converge now converge faster. It's worked like that every time I've tried it — on images. When we tried it on binaries it actually had the opposite effect: networks that converged slowly now didn't at all, no matter what variety of architecture we tried. It's also had no effect at all on some other esoteric data sets that I've worked on.

We discuss this at more length in the paper (§5.3), but here's the relevant figure:

BatchNorm activations
KDE plots of the convolution response (pre-ReLU) for multiple architectures. Red and orange: two layers of ResNet; green: Inception-v4; blue: our network; black dashed: a true Gaussian distribution for reference.

This is showing the pre-BN activations from MalConv (blue) and from ResNet (red & orange) and Inception-v4 (green). The purpose of BatchNorm is to output values in a standard normal, and it implicitly expects inputs that are relatively close to that. What we suspect is happening is that the input values from other networks aren't gaussian, but they're close-ish.2 The input values for MalConv display huge asperity, and aren't even unimodal. If BatchNorm is being wonky for you, I'd suggest plotting the pre-BN activations and checking to see that they're relatively smooth and unimodal.

3. The Lump of Regularization Fallacy

If you're overfitting, you probably need more regularization. Simple advice, and easily executed. Everytime I see this brought up though, people treat regularization as if it's this monolithic thing. Implicitly, people are talking as if you have some pile of regularization, and if you need to fight overfitting then you just shovel more regularization on top. It doesn't matter what kind, just add more.

We ran in to overfitting problems and tried every method we could think of: weight decay, dropout, regional dropout, gradient noise, activation noise, and on and on. The only one that had any impact was DeCov, which penalized activities in the penultimate layer that are highly correlated with each other. I have no idea what will work on your data — especially if it's not images/speech/text — so try different types. Don't just treat regularization as a single knob that you crank up or down.

I hope some of these lessons are helpful to you if you're into cybersecurity, or pushing machine learning into new domains in general. We'll be presenting the paper this is all based on at the Artificial Intelligence for Cyber Security (AICS) workshop at AAAI in February, so if you're at AAAI then stop by and talk.

  1. Everything is related, but near things are more related than far things. []
  2. I'd love to be able to quantify that closeness, but every test for normality I'm aware of doesn't apply when you have this many samples. If anyone knows of a more robust test please let me know. []
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Reading List for 16 July 2013

Evan Miller :: Winkel Tripel Warping Trouble or "How I Found a Bug in the Journal of Surveying Engineering"

All programming blogs need at least one post unofficially titled “Indisputable Proof That I Am Awesome.” These are usually my favorite kind of read, as the protagonist starts out with a head full of hubris, becomes mired in self-doubt, struggles on when others would have quit, and then ultimately triumphs over evil (that is to say, slow or buggy computer code), often at the expense of personal hygiene and/or sanity.

I'm a fan of the debugging narrative, and this is a fine example of the genre. I've been wrestling with code for mapping projections recently, so I feel Miller's pain specifically. In my opinion the Winkel Tripel is mathematically gross, but aesthetically unsurpassed. Hopefully I'll find some time in the next week or so to put up a post about my mapping project.

Irene Global Tweets WInkel Tripel
A screenshot of a project I've been working on to map geotagged tweets.

Kevin Grier :: Breaking down the higher ed wage premium

wage premium by major
Wage premium and popularity of majors

File under "all college degrees are not created equal" or perhaps "no, junior, you may not borrow enough to buy a decent house in order to get a BA in psych."

Aleatha Parker-Wood :: One Shot vs Iterated Games

Social cohesion can be thought of as a manifestation of how "iterated" people feel their interactions are, how likely they are to interact with the same people again and again and  have to deal with long term consequences of locally optimal choices, or whether they feel they can "opt out" of consequences of interacting with some set of people in a poor way.

Mike Munger :: Grade Inflation? Some data

Munger links to some very good analysis but it occurs to me that what is really needed is the variance of grades over time and not just the mean. (Obviously these two things are related since the distribution is bounded by [0, 4]. A mean which has gone from 2.25 to 3.44 will almost certainly result in less variance here.)

I don't much care where the distribution is centered. I care how wide the distribution is — that's what lets observers distinguish one student from another. Rankings need inequality. Without it they convey no information.

Marginal Revolution :: Alex Tabarrok :: The Battle over Junk DNA

I share Graur's and Tabarrok's wariness over "high impact false positives" in science. This is a big problem with no clear solutions.

The Graur et al. paper that Tabarrok discusses is entertaining in its incivility. Sometimes civility is not the correct response to falsehoods. It's refreshing to see scientists being so brutally honest with their opinions. Some might say they are too brutal, but at least they've got the honest part.

Peter McCaffrey :: 5 reasons price gouging should be legal: Especially during disasters

McCaffrey is completely right. But good luck to him reasoning people out of an opinion they were never reasoned into in the first place.

I do like the neologism "sustainable pricing" that he introduces. Bravo for that.

I would add a sixth reason to his list: accusations of "price gouging" are one rhetorical prong in an inescapable triple bind. A seller has three MECE choices: price goods higher than is common, the same as is common, or lower than is common. These choices will result in accusations of price gouging, collusion, and anti-competitive pricing, respectively. Since there is no way to win when dealing with people who level accusations of gouging, the only sensible thing to do is ignore them.

Shawn Regan :: Everyone calm down, there is no “bee-pocalypse”

Executive summary: apiarists have agency, and the world isn't static. If the death rate of colonies increases, they respond by creating more colonies. Crisis averted.

Eliezer Yudkowsky :: Betting Therapy

"Betting Therapy" should be a thing. You go to a betting therapist and describe your fears — everything you're afraid will happen if you do X — and then the therapist offers to bet money on whether it actually happens to you or not. After you lose enough money, you stop being afraid.

Sign me up.

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