On Thu, 2015-01-29 at 20:21 +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 <a...@ozlabs.ru>
> ---
> Changes:
> v5:
> * check is done for all page sizes now, not just for huge pages
> * failed check returns EFAULT now (was EINVAL)
> * moved the check to VFIO SPAPR IOMMU driver
> ---
> 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 dc4a886..99b98fa 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -47,6 +47,22 @@ struct tce_container {
> bool enabled;
> };
>
> +static bool tce_check_page_size(struct page *page, unsigned page_shift)
What does true/false mean for a "check page size" operation? Does true
mean good? Bad? How about naming it page-is-contained or something
along those lines?
> +{
> + 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;
> +}
> +
> static int tce_iommu_enable(struct tce_container *container)
> {
> int ret = 0;
> @@ -199,6 +215,12 @@ static long tce_iommu_build(struct tce_container
> *container,
> ret = -EFAULT;
> break;
> }
> +
> + if (!tce_check_page_size(page, tbl->it_page_shift)) {
> + ret = -EFAULT;
> + break;
> + }
> +
> hva = (unsigned long) page_address(page) +
> (tce & IOMMU_PAGE_MASK(tbl) & ~PAGE_MASK);
>
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