Hacker News new | past | comments | ask | show | jobs | submit
victorbjorklund | on: AI is forcing us to pay off 40 years of technical debt
Explain? (Genuine question because I wanna know)
GTP | parent | next
Basically, have an explicit distinction between data and code at the architectural level, to enforce "Write xor Execute" in hardware. In this way, you would prevent e.g. a buffer overflow letting an attacker injecting shellcode that gets executed later by somehow pointing at it. AFAIK the issue would still remain with some programming languages though.
sznio | root | parent | next
don't we already have the NX bit?

and it's not sufficient anyways. even with NX you could have the attacker control a function pointer you call. in any sufficiently complex program you'll have enough widgets to build anything you want just out of data.

code and data are the same thing. whatever inputs your system receives is "code" that your application interprets, just like your application is the code that the CPU interprets. turtles all the way down.

intrasight | root | parent | next
In a Harvard architecture, it's not possible to point the CPU at data.
loading story #50376883
loading story #50371103
loading story #50369095
ihavesomeexampl | root | parent | next
But.. alter data that gets executed (interpeter?), I mean, how does this work even in theory? All data is potentially code?
AdamH12113 | root | parent | next
To clarify what intrasight is talking about: A Harvard architecture CPU has two physically separate memory busses for code and data. This makes it possible to build a computer with a program memory that cannot be altered through the data bus. In practice, this isn't normally done -- even on Harvard architecture microcontrollers, the flash and RAM are connected to both busses because memory is expensive. And having inalterable program memory doesn't save you from stack-smashing attacks that alter a return address.
intrasight | root | parent
All data is potentially code only in a Von Neumann architecture, but not in a Harvard architecture, where there's a separation of data and code with different memory access to each.
loading story #50366219
lelanthran | root | parent
> All data is potentially code only in a Von Neumann architecture, but not in a Harvard architecture, where there's a separation of data and code with different memory access to each.

Says you. I wrote a program for a Hardvard architecture chip (PIC) that read bytecode from the data memory and executed it. Updates were made by replacing the data block with a new data block.

In practice, there is no way to separate data and instructions. After all, JS downloaded inside a webpage is literally data, and it gets executed.

tosapple | root | parent | next
and we don't believe a sterilized virtual machine creates a similar situation?

any respective machine doesn't require full Turing completeness?

any ad-hoc machine allows for mutations and flexibility, which I'm sure is an added strength.

2nd edit,

Also, didn't we have a weaker model of this with segmented non-flat memory models on i386-

AlienRobot | root | parent
How do you turn text into code in this architecture? Through the kernel?
SSLy | root | parent
you don't. I also believe that JITs would be impossible under strict Harvard.
loading story #50370276