Subject: Re: [PATCH kernel v10 07/34] vfio: powerpc/spapr: Check that IOMMU page is fully contained by system page

From: Gavin Shan <[email-masked]>
Date: Wed, 13 May 2015 16:06:47 +1000

On Tue, May 12, 2015 at 01:38:56AM +1000, 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 <[email-masked]>
>[aw: for the vfio related changes]
>Acked-by: Alex Williamson <[email-masked]>
>Reviewed-by: David Gibson <[email-masked]>

Reviewed-by: Gavin Shan <[email-masked]>

Thanks,
Gavin

>---
>Changes:
>v8: changed subject
>
>v6:
>* the helper is simplified to one line
>
>v4:
>* s/tce_check_page_size/tce_page_is_contained/
>---
> drivers/vfio/vfio_iommu_spapr_tce.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
>diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>index b95fa2b..735b308 100644
>--- a/drivers/vfio/vfio_iommu_spapr_tce.c
>+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>@@ -47,6 +47,16 @@ struct tce_container {
> 	bool enabled;
> };
>
>+static bool tce_page_is_contained(struct page *page, unsigned page_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.
>+	 */
>+	return (PAGE_SHIFT + compound_order(compound_head(page))) >= page_shift;
>+}
>+
> static int tce_iommu_enable(struct tce_container *container)
> {
> 	int ret = 0;
>@@ -189,6 +199,12 @@ 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) + offset;
>
> 		ret = iommu_tce_build(tbl, entry + i, hva, direction);
>-- 
>2.4.0.rc3.8.gfb3e7d5
>