Re: [Xen-devel] [PATCH v1 9/9] mm: Make sure pages are scrubbed

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Mar 29, 2017 at 12:35:25PM -0400, Boris Ostrovsky wrote:
> On 03/29/2017 12:25 PM, Wei Liu wrote:
> > On Fri, Mar 24, 2017 at 01:05:04PM -0400, Boris Ostrovsky wrote:
> >> +static void check_one_page(struct page_info *pg)
> >> +{
> >> +    mfn_t mfn = _mfn(page_to_mfn(pg));
> >> +    uint64_t *ptr;
> >> +
> >> +    ptr  = map_domain_page(mfn);
> >> +    ASSERT(*ptr != PAGE_POISON);
> > Should be ASSERT(*ptr == 0) here.
> 
> We can't assume it will be zero --- see scrub_one_page().

It's still possible a value is leaked from the guest, and that value has
rather high probability to be != PAGE_POISON.

In that case there should be a ifdef to match the debug and non-debug
builds.

Wei.

> 
> -boris

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