Messages in this thread | | | Date | Mon, 9 Jan 2023 11:47:21 +0000 | Subject | Re: [PATCH] iommu/iova: Fix alloc iova overflows issue | From | Robin Murphy <> |
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On 2023-01-09 08:34, yf.wang@mediatek.com wrote: > From: Yunfei Wang <yf.wang@mediatek.com> > > In __alloc_and_insert_iova_range, there is an issue that retry_pfn > overflows. The value of iovad->anchor.pfn_hi is ~0UL, then when > iovad->cached_node is iovad->anchor, curr_iova->pfn_hi + 1 will > overflow. As a result, if the retry logic is executed, low_pfn is > updated to 0, and then new_pfn < low_pfn returns false to make the > allocation successful. > > This issue occurs in the following two situations: > 1. The first iova size exceeds the domain size. When initializing > iova domain, iovad->cached_node is assigned as iovad->anchor. For > example, the iova domain size is 10M, start_pfn is 0x1_F000_0000, > and the iova size allocated for the first time is 11M. The > following is the log information, new->pfn_lo is smaller than > iovad->cached_node. > > Example log: > [ 223.798112][T1705487] sh: [name:iova&]__alloc_and_insert_iova_range > start_pfn:0x1f0000,retry_pfn:0x0,size:0xb00,limit_pfn:0x1f0a00 > [ 223.799590][T1705487] sh: [name:iova&]__alloc_and_insert_iova_range > success start_pfn:0x1f0000,new->pfn_lo:0x1efe00,new->pfn_hi:0x1f08ff > > 2. The node with the largest iova->pfn_lo value in the iova domain > is deleted, iovad->cached_node will be updated to iovad->anchor, > and then the alloc iova size exceeds the maximum iova size that can > be allocated in the domain. > > Adding judgment that retry_pfn must be greater than iovad->start_pfn > can fix this issue.
Hmm, indeed that's a sneaky little bug - thanks for the thorough analysis - but couldn't we avoid the overflow entirely? I don't have the complete logic paged in, but superficially it seems like:
retry_pfn = curr_iova->pfn_hi; ... retry_pfn <= limit_pfn ... low_pfn = retry_pfn + 1;
should still work, shouldn't it?
Thanks, Robin.
> Signed-off-by: jianjiao zeng <jianjiao.zeng@mediatek.com> > Signed-off-by: Yunfei Wang <yf.wang@mediatek.com> > --- > drivers/iommu/iova.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index a44ad92fc5eb..0073206c2a95 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -209,7 +209,8 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad, > } while (curr && new_pfn <= curr_iova->pfn_hi && new_pfn >= low_pfn); > > if (high_pfn < size || new_pfn < low_pfn) { > - if (low_pfn == iovad->start_pfn && retry_pfn < limit_pfn) { > + if (low_pfn == iovad->start_pfn && > + retry_pfn >= iovad->start_pfn && retry_pfn < limit_pfn) { > high_pfn = limit_pfn; > low_pfn = retry_pfn; > curr = iova_find_limit(iovad, limit_pfn);
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