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authorNate Watterson <nwatters@codeaurora.org>2017-04-07 01:36:20 -0400
committerJoerg Roedel <jroedel@suse.de>2017-04-07 13:40:40 +0200
commit5016bdb796b3726eec043ca0ce3be981f712c756 (patch)
tree6f8b910fd9e65d6f893b7b43883bad5230d98228 /drivers
parentbb65a64c7285e7105c1a6c8a33b37770343a4e96 (diff)
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 <nwatters@codeaurora.org> Signed-off-by: Joerg Roedel <jroedel@suse.de>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/iommu/iova.c2
1 files changed, 1 insertions, 1 deletions
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);