[lowrisc-dev] New security concept: Seperated Stack

Philipp Gühring pg at futureware.at
Fri Feb 20 22:26:11 GMT 2015


I have an idea that I would like to contribute to LowRISC:
Seperated Stacks.
The problem I see with most current CPU´s and software stacks running on
them is that they have merged the program stack and the data stack into a
single stack. This results in various problems like stack overflows, stack
underflows, return-oriented programming and various other exploits.
My idea is to seperate the program stack (which would just contain the
fixed size return addresses) from the data stack (which would contain the
data), and put them into different segments. 
>From my experience, most exploits are overflowing/underflowing the data
stack, not the code stack. So by simply seperating both stacks, you can
protect the code stack from any exploits on the data stack.
I tried to implement a proof-of-concept with Linux and Windows on X86 some
time ago, but it was very hard to find free and reuseable registers for
the seperated stacks on X86.
What I think is necessary is:
* A CodeStack-Segment register
* A CodeStack-StackPointer register
* A DataStack-Segment register
* A DataStack-StackPointer register
* The necessary opcodes to cope with them

If you were able to add those to your LowRISC architecture, and the
compilers would be adapted to make use of the added registers, to generate
code that utilizes seperated stack code, I think that would be a huge step
to protect the whole platform against most of the buffer overflows and

While you are at it, I would also suggest to implement something like
Google Native´s client NACL instruction in hardware.

Best regards,
Philipp Gühring

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