From 5016bdb796b3726eec043ca0ce3be981f712c756 Mon Sep 17 00:00:00 2001 From: Nate Watterson Date: Fri, 7 Apr 2017 01:36:20 -0400 Subject: iommu/iova: Fix underflow bug in __alloc_and_insert_iova_range Normally, calling alloc_iova() using an iova_domain with insufficient pfns remaining between start_pfn and dma_limit will fail and return a NULL pointer. Unexpectedly, if such a "full" iova_domain contains an iova with pfn_lo == 0, the alloc_iova() call will instead succeed and return an iova containing invalid pfns. This is caused by an underflow bug in __alloc_and_insert_iova_range() that occurs after walking the "full" iova tree when the search ends at the iova with pfn_lo == 0 and limit_pfn is then adjusted to be just below that (-1). This (now huge) limit_pfn gives the impression that a vast amount of space is available between it and start_pfn and thus a new iova is allocated with the invalid pfn_hi value, 0xFFF.... . To rememdy this, a check is introduced to ensure that adjustments to limit_pfn will not underflow. This issue has been observed in the wild, and is easily reproduced with the following sample code. struct iova_domain *iovad = kzalloc(sizeof(*iovad), GFP_KERNEL); struct iova *rsvd_iova, *good_iova, *bad_iova; unsigned long limit_pfn = 3; unsigned long start_pfn = 1; unsigned long va_size = 2; init_iova_domain(iovad, SZ_4K, start_pfn, limit_pfn); rsvd_iova = reserve_iova(iovad, 0, 0); good_iova = alloc_iova(iovad, va_size, limit_pfn, true); bad_iova = alloc_iova(iovad, va_size, limit_pfn, true); Prior to the patch, this yielded: *rsvd_iova == {0, 0} /* Expected */ *good_iova == {2, 3} /* Expected */ *bad_iova == {-2, -1} /* Oh no... */ After the patch, bad_iova is NULL as expected since inadequate space remains between limit_pfn and start_pfn after allocating good_iova. Signed-off-by: Nate Watterson Signed-off-by: Joerg Roedel --- drivers/iommu/iova.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/iommu/iova.c') diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index b7268a14184f..f6533e0198f6 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -138,7 +138,7 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad, break; /* found a free slot */ } adjust_limit_pfn: - limit_pfn = curr_iova->pfn_lo - 1; + limit_pfn = curr_iova->pfn_lo ? (curr_iova->pfn_lo - 1) : 0; move_left: prev = curr; curr = rb_prev(curr); -- cgit v1.2.3