Comment by pcwalton | Hacker News Reader

Comment by pcwalton | Hacker News Reader

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> You don't increase the surface area by also sandboxing the PDF plugin -- either the sandboxing mechanism works or it doesn't.

Adding more C++ to the browser certainly does increase the attack area. Sandboxes that expose enough functionality to run a modern browser engine commonly end up with holes here and there (e.g. the Pwnium vulnerabilities) and it's best to not use them as the only layer of defense; moreover, the sandbox does not fully enforce all of the security properties that the Web platform demands (e.g. cross-origin iframes).

> 3. If anything, pdf.js's continued poor performance and operation demonstrates why forcing everyone to operate inside of a JS runtime is incredibly harmful to the web platform's progress.

As I mentioned before, pdf.js is not as JS bound as you might think. Furthermore, it was written before asm.js existed and doesn't use any asm.js; if pdf.js were JS bound, then asm.js would be a very powerful option to improve performance that would not involve dropping to unsafe native code.

The DRM sandbox is yet another attack surface, isn't it? Wouldn't it make sense to use NaCl for DRM sandboxing, and then the option is open to use the same sandbox for PDF viewing, and pdf.js can still work, giving users choice.

Creating yet another sandbox seems silly, and NaCl hasn't been hit by pwnium, it's only been a stepping stone to the renderer (I'll let comex dive into details here!)

NaCl is not exactly a stepping stone to the renderer. NaCl modules live outside the renderer process in a much tighter sandbox that uses control flow integrity and software fault isolation. Gaining code execution within the NaCl sandbox (easy since you can just send the user a NaCl module) does not expose the same attack surface as gaining code execution within a renderer process.

Well, the DRM sandbox has very few exposed APIs, in contrast to the Web sandbox or Pepper.

I don't like the DRM sandbox anyhow; it's unfortunate that DRM was added to the Web, forcing a DRM module at all (speaking for myself, not my employer).

I discussed this with Alon on IRC: you wouldn't use pepper to do this. NaCl doesn't imply pepper, you can expose a subset of syscalls into the trusted code base.

I understand the feeling about DRM, but given that sandboxed DRM is going to happen I'd hope that the best efforts possible are put in to make users safe. Good sandboxing seems the right way to go. I'm not any kind of a security expert, but jschuh seems to think the current sandbox isn't sufficient: https://bugzilla.mozilla.org/show_bug.cgi?id=1011491 I hope the right improvements go into tightening the DRM sandbox :)

Hey, side question: I assume pdfium runs in the NaCl sandbox - how does that work with v8?

Sorry, I don't check HN often. As we discussed on Twitter & IRC:

It's just an OS sandbox currently. pdfium previously worked with NaCl, with a non-V8 JS VM (work done by Bill Budge). V8-on-NaCl used to work, I think it may have bitrotted since then, but it used NaCl's dyncode modify API to do PIC. The GC moves code too, so extra page permissions need to be changed when that's done, but I think that's the extent of code modification that needs to be handled for a JS JIT to work on NaCl (on top of the sandboxing).

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