linux-kernel - Re: [PATCH v5 03/29] vfio: powerpc/spapr: Check that TCE page size is equal to it_page

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Date:	Tue, 10 Mar 2015 17:03:26 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	linuxppc-dev@...ts.ozlabs.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 03/29] vfio: powerpc/spapr: Check that TCE page size
 is equal to it_page_size

On Wed, 2015-03-11 at 09:57 +1100, Alexey Kardashevskiy wrote:
> On 03/11/2015 06:56 AM, Alex Williamson wrote:
> > On Tue, 2015-03-10 at 01:06 +1100, Alexey Kardashevskiy wrote:
> >> This checks that the TCE table page size is not bigger that the size of
> >> a page we just pinned and going to put its physical address to the table.
> >>
> >> Otherwise the hardware gets unwanted access to physical memory between
> >> the end of the actual page and the end of the aligned up TCE page.
> >>
> >> Since compound_order() and compound_head() work correctly on non-huge
> >> pages, there is no need for additional check whether the page is huge.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
> >> ---
> >> Changes:
> >> v4:
> >> * s/tce_check_page_size/tce_page_is_contained/
> >> ---
> >>   drivers/vfio/vfio_iommu_spapr_tce.c | 22 ++++++++++++++++++++++
> >>   1 file changed, 22 insertions(+)
> >>
> >> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> >> index 756831f..91e7599 100644
> >> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> >> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> >> @@ -49,6 +49,22 @@ struct tce_container {
> >>   	bool enabled;
> >>   };
> >>
> >> +static bool tce_page_is_contained(struct page *page, unsigned page_shift)
> >> +{
> >> +	unsigned shift;
> >> +
> >> +	/*
> >> +	 * Check that the TCE table granularity is not bigger than the size of
> >> +	 * a page we just found. Otherwise the hardware can get access to
> >> +	 * a bigger memory chunk that it should.
> >> +	 */
> >> +	shift = PAGE_SHIFT + compound_order(compound_head(page));
> >> +	if (shift >= page_shift)
> >> +		return true;
> >> +
> >> +	return false;
> >
> > nit, simplified:
> >
> > return (PAGE_SHIFT + compound_order(compound_head(page) >= page_shift);
> 
> This won't be "bool" though.

Yes, it will.

>  This will (I'll do this)
> 
> shift = PAGE_SHIFT + compound_order(compound_head(page));
> return (shift >= page_shift);
> 
> 
> 
> 
> >
> >> +}
> >> +
> >>   static int tce_iommu_enable(struct tce_container *container)
> >>   {
> >>   	int ret = 0;
> >> @@ -197,6 +213,12 @@ static long tce_iommu_build(struct tce_container *container,
> >>   			ret = -EFAULT;
> >>   			break;
> >>   		}
> >> +
> >> +		if (!tce_page_is_contained(page, tbl->it_page_shift)) {
> >> +			ret = -EPERM;
> >> +			break;
> >> +		}
> >> +
> >>   		hva = (unsigned long) page_address(page) +
> >>   			(tce & IOMMU_PAGE_MASK(tbl) & ~PAGE_MASK);
> >>
> >
> >
> >
> 
> 



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