4 ms·

Thankfully Apple can, in principle, statically analyze for this on the iOS App Store, as they do not allow JIT mappings on those devices.

• e_proxus 5y ago
  Can they guarantee no JIT code via static analysis as well? Or could someone sneak in a tiny bit of disguised JIT code just to get to this register? I would assume a huge JITed VM implementation would show up easily in analysis.
  • phire 5y ago
    They don't provide anyway to mark memory as executable.
    • saagarjha 5y ago
      Well, they do, because they have to run your code :P You just can't make a new page of code and mark it executable.
      • marcan_42 5y ago
        The OS only makes pages executable if they come from a signed app. There is no way for the app itself to do that.
        • saagarjha 5y ago
          If it makes it more clear, my comment was mostly "if your code page has a valid signature you can mark it as executable".
  • deleted 5y ago
    [deleted]
• tyingq 5y ago
  Do you need JIT though? Does Xcode support inline ASM, or various compilers extensions that can read/write a cpu register?
  • marcan_42 5y ago
    If you put this in your app directly, Apple can just find it and reject it at submission time. If JIT were an option, that wouldn't be enough, because the app could do it at runtime. Since it isn't, there is no way to "hide" something like this from the App Store static analyzer.
    • tyingq 5y ago
      Hrm. It seems like inline ASM allows for passing the register name dynamically, though I can't tell for sure. If that's the case, it seems like it would be hard to tell ahead of time, other than "app calls msr/mrs".
      • saagarjha 5y ago
        Inline assembly must resolve register names at compile time.