Re: virtualization, Constant Stack Canaries

On 4/16/2025 6:04 PM, John Levine wrote:

According to Scott Lurndal <slp53@pacbell.net>:

I think you could gain a tiny amount of efficiency if the OS (super)
allowed the user to set up handle certain classes of exceptions, e.g.
divide faults) itself rather than having to go through the super.

>
Think carefully about the security implications of user-mode interrupt
delivery.  Particuarly with respect to potential impacts on other
processes running on the system, and to overall system functionality.
>
Handling interrupts requires direct access to the hardware from
user-mode.

 I think he was talking about exceptions, not interrupts.

Right.  Thanks John.  I was careful to say exceptions, not interrupts.

I don't see much
danger in reflecting divide faults and supervisor calls directly back
to the virtual machine.  I gather that IBM's virtualization microcode has
done that for decades.

I was suggesting that for things like divide fault, it could go directly back to the user, assuming the user had set up a place to handle them.

 External interrupts are indeed a lot harder unless you know a whole lot
about the thing that's interrupting.

Yup.
--
  - Stephen Fuld
(e-mail address disguised to prevent spam)