Re: [PATCH 1/3] KVM: x86 emulator: Fix task switch privilege checks

[Gleb Natapov <gleb@redhat.com>]

On Tue, Jan 24, 2012 at 03:15:13PM +0100, Kevin Wolf wrote:
> Am 24.01.2012 15:03, schrieb Joerg Roedel:
> > On Mon, Jan 23, 2012 at 05:10:46PM +0100, Kevin Wolf wrote:
> >> This patch fixes the problem for VMX. For SVM, the logic used to
> >> determine the source of the task switch is buggy, so we can't pass
> >> useful information to the emulator there and just disable the check in
> >> all cases.
> > 
> > Actually, SVM isn't buggy :) For SVM you do not need to do any
> > priviledge checks in software because the hardware already takes care of
> > that.
> > In other words, KVM only gets a task-switch intercept if the priviledges
> > are all checked and correct.
> 
> Okay, that's good to hear. The current code is still buggy because as
> Gleb noted it checks against the TSS DPL. We need to disable that check
> for SVM then. Also all checks for TASK_SWITCH_GATE indicate that
> something is wrong because it will never happen.
> 
Not necessary. Currently all checks for TASK_SWITCH_GATE also check for
TASK_SWITCH_CALL, so I think you can fix SVM case in your patch by
passing TASK_SWITCH_GATE instead of TASK_SWITCH_CALL to
kvm_task_switch().

> Are you going to rewrite task_switch_interception() on top of this series?
> 
> Kevin

--
			Gleb.