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From: John Levine <johnl@taugh.com>
Newsgroups: comp.arch
Subject: Re: virtualization, Constant Stack Canaries
Date: Thu, 17 Apr 2025 01:04:10 -0000 (UTC)
Organization: Taughannock Networks
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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.  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.

External interrupts are indeed a lot harder unless you know a whole lot
about the thing that's interrupting.
-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly