Re: stack protection in mini-os

[Samuel Thibault <samuel.thibault@eu.citrix.com>]

Hello,

For stubdomains, what I did is to add a check for ESP relative to the
bottom of the stack in a frequently called function, (think about
something like errno_location())

Harald Roeck, le Thu 31 Jul 2008 13:58:36 -0700, a écrit :
> If we overflow the stack and run into the
> mapped out stack page xen crashes and the machine reboots.

Uh, that's bad! Which version of Xen is this with? That is a bug of Xen,
can you reproduce it with a RC of 3.3?

> it looks like xen is trying to push the arguments for the page fault
> trap onto the mapped out page.

Most probably yes, but it should catch the error.

> rbp: 000000000007b120   rsp: 000000000007aff0   r8:  0000000000000010
> ...
> 
> fyi: the read only page in this setup was 0x7a000.

So that's coherent indeed, but I guess you'd like to have the backtrace.

> so my question: is it possible to set an "alternate" trap stack?

I don't think the hypervisor provides this for kernel level.

> or the failsafe_callback?

failsafe_callback is only called when you get a fault during the
execution of callback, not during normal flow.

Samuel