[PATCH 2/3] iommu/iova: Make rcache limit_pfn handling more robust

[Robin Murphy <robin.murphy@arm.com>]

When popping a pfn from an rcache, we are currently checking it directly
against limit_pfn for viability. Since this represents iova->pfn_lo, it
is technically possible for the corresponding iova->pfn_hi to be greater
than limit_pfn. Although we generally get away with it in practice since
limit_pfn is typically a power-of-two boundary and the IOVAs are
size-aligned, it's pretty trivial to make the iova_rcache_get() path
take the allocation size into account for complete safety.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/iova.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 35dde0fc7793..8f8b436afd81 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -411,7 +411,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
 	unsigned long iova_pfn;
 	struct iova *new_iova;
 
-	iova_pfn = iova_rcache_get(iovad, size, limit_pfn);
+	iova_pfn = iova_rcache_get(iovad, size, limit_pfn + 1);
 	if (iova_pfn)
 		return iova_pfn;
 
@@ -828,7 +828,7 @@ static unsigned long iova_magazine_pop(struct iova_magazine *mag,
 {
 	BUG_ON(iova_magazine_empty(mag));
 
-	if (mag->pfns[mag->size - 1] >= limit_pfn)
+	if (mag->pfns[mag->size - 1] > limit_pfn)
 		return 0;
 
 	return mag->pfns[--mag->size];
@@ -982,7 +982,7 @@ static unsigned long iova_rcache_get(struct iova_domain *iovad,
 	if (log_size >= IOVA_RANGE_CACHE_MAX_SIZE)
 		return 0;
 
-	return __iova_rcache_get(&iovad->rcaches[log_size], limit_pfn);
+	return __iova_rcache_get(&iovad->rcaches[log_size], limit_pfn - size);
 }
 
 /*
-- 
2.13.4.dirty