Subject: Re: [PATCH v5 03/29] vfio: powerpc/spapr: Check that TCE page size is equal to it_page_size

From: Alexey Kardashevskiy <[email-masked]>
Date: Wed, 11 Mar 2015 09:57:56 +1100

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 <[email-masked]>
>> ---
>> 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. 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);
>>
>
>
>

-- 
Alexey