Re: [Xen-devel] [PATCH] xen/kexec: Clear unused registers before jumping into an image

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.11.13 at 21:07, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> On 15/11/13 15:56, Daniel Kiper wrote:
>> Clear unused registers before jumping into an image. This way
>> loaded image could not assume that any register has an specific
>> info about earlier running Xen hypervisor. However, it also
>> does not mean that the image may expect that a given register
>> is zeroed. The image MUST assume that every register has a random
>> value or in other words it is uninitialized or has undefined state.
> 
> I think this, where the specification (registers undefined) differs from
> the implementation (registers zeroed), is the worst option.
> 
> I also think it is more likely for an image to inadvertently rely on a
> zero value that whatever junk Xen has left behind.

Preventing users to rely on anything would likely make it
desirable to put some random value into all unused registers.

Jan


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