Re: [Qemu-devel] qemu allows code execution on the stack, even if the quest operating system makes the stack nonexecutable

[Fabrice Bellard]

If CS.limit is used to implement non executable memory, it is normal 
because QEMU does not test segment limits for performance reasons.

QEMU will someday implement PAE and NX bits - it is the most efficient 
way to handle this.

Fabrice.

joro 42 wrote:
> tested openwall linux and openbsd 3.5 under qemu.
> both of them claim to make the stack non executable when on real x86.
>
> but under qemu, code on the stack seems executed on owl and obsd3.5.
>
> try the following program:
>
> ===========
> void main()
> {
>         char trap[]="\xcc"; // "\xeb\xfe" for loop
>         void (*f)();
>         f=trap;
>         f();
> }
> ===========
>
> it executes code instead of SEGV on openwall/openbsd.
>
> /j