4.4-stable review patch. If anyone has any objections, please let me know.
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From: Nate Watterson nwatters@codeaurora.org
[ Upstream commit 5016bdb796b3726eec043ca0ce3be981f712c756 ]
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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/iommu/iova.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -126,7 +126,7 @@ static int __alloc_and_insert_iova_range 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);