The security model for nacl is afaik that you run almost arbitrary native code. It was compiled by someone else, your input is basically machine code that you d

The security model for nacl is afaik that you run almost arbitrary native code. It was compiled by someone else, your input is basically machine code that you don't know anything about except for some please-dont-break-my-sandbox checks. With asm.js, your input is javascript code which can't do all the weird things that native code can do, and you're in charge of generating the native code that ultimately gets executed (much like the traditional JIT setup), so assuming you didn't fuck up the translation, you get to assume it can't do anything that javascript code couldn't have done to begin with, relaxing your sandboxing requirements around, like, arbitrary memory accesses or syscalls.