Re: [Xen-devel] Invalid VA => ptr conversion with xc_dom_* API after XSA-55 fox

["Jean-Yves Migeon (NetBSD)" <jym@xxxxxxxxxx>]

Le 25/11/2013 12:44, Ian Jackson a ÃcritÂ:
> Jan Beulich writes ("Re: [Xen-devel] Invalid VA => ptr conversion
> with xc_dom_* API after XSA-55 fox"):
> > On 20.11.13 at 13:56, "Jean-Yves Migeon (NetBSD)" <jym@xxxxxxxxxx> 
> > wrote:
> > > Jeff and FastIce pointed out a regression between Xen 4.1.2 and 
> > 4.1.6
> > > when starting NetBSD domU; the kernel syms table gets slightly 
> > corrupted
> > > [1].
> > >
> > > After dwelling into libxc code, FastIce noticed that changing back 
> > the
> > > return value to "ptr + offset" (instead of just "ptr") for
> > > xc_dom_vaddr_to_ptr() makes it work again.
> > >
> > > According to [2] while fixing XSA-55, Ian changed the "ptr + 
> > offset"
> > > return value to just "ptr". Is there a reason for this? IMHO the 
> > VA =>
> > > ptr conversion should also take into account non-page aligned 
> > addresses,
> > > hence the offset (except for NULL value of course).
> >
> > I agree, but let's see what Ian (being the author of the whole
> > patch set) says.
> It looks like I changed this in b5a86920.  Having stared at the code
> and the commit message I think that I did in fact break this, by
> inadvertantly removing the "+ offset".  Sorry to cause a regression.
>
> I've examined the surrounding code and reread the relevant bits of
> xc_dom_pfn_to_ptr_retcount and I think that simpy returning
> "ptr + offset" is the correct fix.  The calculation of
> *safe_region_out is already correct.
>
> Will someone write this up as a patch submission ?
Will do (tonight).

> In any case, the fix ought to be backported.
>
> Thanks,
Thanks for your review!

Cheers,

--
Jean-Yves Migeon
jym@

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