Re: [PATCH v3 01/11] xen/manage: keep track of the on-going suspend mode

From: Boris Ostrovsky
Date: Thu Jun 03 2021 - 21:50:30 EST

On 6/3/21 7:27 PM, Anchal Agarwal wrote:
> On Thu, Jun 03, 2021 at 04:11:46PM -0400, Boris Ostrovsky wrote:
>> But if KASLR is on then this comparison not failing should cause xen_vcpu pointer in the loaded image to become bogus because xen_vcpu is now registered for a different xen_vcpu_info address during boot.
> The reason for that I think is once you jump into the image that information is
> getting lost. But there is some residue somewhere that's causing the resume to
> fail. I haven't been able to pinpoint the exact field value that may be causing
> that issue.

xen_vcpu now points to address which is not where the hypervisor thinks vcpu_info should be.

> Correct me if I am wrong here, but even if hypothetically I put a hack to tell the kernel
> somehow re-register vcpu it won't pass because there is no hypercall to
> unregister it in first place?

Right. You will be shown the door in map_vcpu_info():

       if ( !mfn_eq(v->vcpu_info_mfn, INVALID_MFN) )
           return -EINVAL;

> Can the resumed kernel use the new values in that
> case [Now this is me just throwing wild guesses!!]

I don't think so --- hypervisor is now pointing to a random location in your image.