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Re: [Qemu-devel] [PATCH 5/5] Port apic to new VMState design


From: Reimar Döffinger
Subject: Re: [Qemu-devel] [PATCH 5/5] Port apic to new VMState design
Date: Tue, 18 Aug 2009 16:24:43 +0200
User-agent: Mutt/1.5.20 (2009-06-14)

Hello,
sorry for replying in the middle of the thread, I was to fast and
deleted the other mails already.
And just in case I mention I am new around here, so feel free to ignore
me if you feel I am completely wrong.
One thing I don't like too much about it is that you can't really handle
"calculated" fields. It seems qemu does not use this (much/yet?), but
it seems good design to me that when a device emulation can handle
multiple devices, you store in one place the device name but to avoid
switch...case in lots of places you also have capability flags stored
somewhere.
Saving both seems a bit like a bad design: the value of one implies the
exact value of the other, so it is at least pointless.
More importantly (though I do not know if qemu intends to care about
this) it might be able to hand-craft a saved vm that after loading then
violates some assumptions of the emulation code, possibly being
exploitable.
If nothing else, I'd at least add support for a "verify" function that
gets a "const state *" and can abort loading the VM in case someone
tries something evil (or can print some useful hint instead of having
qemu crash silently on the user, possibly at some later time).
And yes I see that today almost nothing (of what I saw) verifies
anything, but it feels wrong to me to code that into a API design.

Greetings,
Reimar Döffinger




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