Messages in this thread | | | Date | Thu, 26 May 2011 13:46:11 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering |
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On 05/26/2011 01:38 PM, Ingo Molnar wrote: > * Gleb Natapov<gleb@redhat.com> wrote: > > > On Thu, May 26, 2011 at 11:57:51AM +0300, Pekka Enberg wrote: > > > Hi Avi, > > > > > > On Thu, May 26, 2011 at 11:49 AM, Avi Kivity<avi@redhat.com> wrote: > > > > > > > You mean each thread will have a different security context? I > > > > don't see the point. All threads share all of memory so it > > > > would be trivial for one thread to exploit another and gain all > > > > of its privileges. > > > > > > So how would that happen? I'm assuming that once the security > > > context has been set up for a thread, you're not able to change > > > it after that. You'd be able to exploit other threads through > > > shared memory but how would you gain privileges? > > > > By tricking other threads to execute code for you. Just replace > > return address on the other's thread stack. > > That kind of exploit is not possible if the worker pool consists of > processes - which would be rather easy to achieve with tools/kvm/. > > In that model each process has its own stack, not accessible to other > worker processes. They'd only share the guest RAM image and some > (minimal) global state. > > This way the individual devices are (optionally) isolated from each > other. In a way this is a microkernel done right ;-)
It's really hard to achieve, since devices have global interactions. For example a PCI device can change the memory layout when a BAR is programmed. So you would have a lot of message passing going on (not at runtime, so no huge impact on performance). The programming model is very different.
Note that message passing is in fact quite a good way to model hardware, since what different devices actually do is pass messages to each other. I expect if done this way, the device model would be better than what we have today. But it's not an easy step away from threads.
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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