[PATCH 3.16 006/254] iommu/vt-d: Fix scatterlist offset handling

Ben Hutchings
2018-02-28T15:32:24Z

From: Robin Murphy <robin.murphy@arm.com>

commit 29a90b70893817e2f2bb3cea40a29f5308e21b21 upstream.

The intel-iommu DMA ops fail to correctly handle scatterlists where
sg->offset is greater than PAGE_SIZE - the IOVA allocation is computed
appropriately based on the page-aligned portion of the offset, but the
mapping is set up relative to sg->page, which means it fails to actually
cover the whole buffer (and in the worst case doesn't cover it at all):

(sg->dma_address + sg->dma_len) ----+
sg->dma_address ---------+ |
iov_pfn------+ | |
| | |
v v v
iova: a b c d e f
|--------|--------|--------|--------|--------|
<...calculated....>
[_____mapped______]
pfn: 0 1 2 3 4 5
|--------|--------|--------|--------|--------|
^ ^ ^
| | |
sg->page ----+ | |
sg->offset --------------+ |
(sg->offset + sg->length) ----------+

As a result, the caller ends up overrunning the mapping into whatever
lies beyond, which usually goes badly:

[ 429.645492] DMAR: DRHD: handling fault status reg 2
[ 429.650847] DMAR: [DMA Write] Request device [02:00.4] fault addr f2682000 ...

Whilst this is a fairly rare occurrence, it can happen from the result
of intermediate scatterlist processing such as scatterwalk_ffwd() in the
crypto layer. Whilst that particular site could be fixed up, it still
seems worthwhile to bring intel-iommu in line with other DMA API
implementations in handling this robustly.

To that end, fix the intel_map_sg() path to line up the mapping
correctly (in units of MM pages rather than VT-d pages to match the
aligned_nrpages() calculation) regardless of the offset, and use
sg_phys() consistently for clarity.

Reported-by: Harsh Jain <Harsh@chelsio.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed by: Ashok Raj <ashok.raj@intel.com>
Tested by: Jacob Pan <jacob.jun.pan@intel.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/iommu/intel-iommu.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2008,10 +2008,12 @@ static int __domain_mapping(struct dmar_
uint64_t tmp;

if (!sg_res) {
+ unsigned int pgoff = sg->offset & ~PAGE_MASK;
+
sg_res = aligned_nrpages(sg->offset, sg->length);
- sg->dma_address = ((dma_addr_t)iov_pfn << VTD_PAGE_SHIFT) + sg->offset;
+ sg->dma_address = ((dma_addr_t)iov_pfn << VTD_PAGE_SHIFT) + pgoff;
sg->dma_length = sg->length;
- pteval = page_to_phys(sg_page(sg)) | prot;
+ pteval = (sg_phys(sg) - pgoff) | prot;
phys_pfn = pteval >> VTD_PAGE_SHIFT;
}

@@ -3345,7 +3347,7 @@ static int intel_nontranslate_map_sg(str

for_each_sg(sglist, sg, nelems, i) {
BUG_ON(!sg_page(sg));
- sg->dma_address = page_to_phys(sg_page(sg)) + sg->offset;
+ sg->dma_address = sg_phys(sg);
sg->dma_length = sg->length;
}
return nelems;