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

From: David Vrabel <david.vrabel@citrix.com>
To: Daniel Kiper <daniel.kiper@oracle.com>
Cc: keir@xen.org, george.dunlap@eu.citrix.com,
	andrew.cooper3@citrix.com, kexec@lists.infradead.org,
	xen-devel@lists.xen.org, ebiederm@xmission.com,
	jbeulich@suse.com
Subject: Re: [PATCH] xen/kexec: Clear unused registers before jumping into an image
Date: Fri, 15 Nov 2013 20:07:02 +0000	[thread overview]
Message-ID: <52867EE6.7080205@citrix.com> (raw)
In-Reply-To: <1384530974-26813-1-git-send-email-daniel.kiper@oracle.com>

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.

David

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