Re: iommu/vt-d: drop mm use count if address is not canonical

Joerg Roedel
2019-04-26T13:38:55Z

[ Adding more people. ]

On Wed, Apr 17, 2019 at 05:12:57PM +0800, Pan Bian wrote:
> The use count of svm->mm is incremented by mmget_not_zero. However, it
> is not dropped when the address is not canonical. This patch fixes the
> bug.
>
> Fixes: 9d8c3af31607("iommu/vt-d: IOMMU Page Request needs to check if
> address is canonical.")
>
> Signed-off-by: Pan Bian <bianpan2016@163.com>
> ---
> drivers/iommu/intel-svm.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
> index 3a4b09a..2630d2e 100644
> --- a/drivers/iommu/intel-svm.c
> +++ b/drivers/iommu/intel-svm.c
> @@ -574,8 +574,10 @@ static irqreturn_t prq_event_thread(int irq, void *d)
> goto bad_req;
>
> /* If address is not canonical, return invalid response */
> - if (!is_canonical_address(address))
> + if (!is_canonical_address(address)) {
> + mmput(svm->mm);
> goto bad_req;
> + }
>
> down_read(&svm->mm->mmap_sem);
> vma = find_extend_vma(svm->mm, address);

I think it is better to move the canonical address check before
mmget_not_zero() like in the diff below. But I let David and Jacob
comment on this.

Regards,

Joerg

diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
index 8f87304f915c..5e9e1eee8336 100644
--- a/drivers/iommu/intel-svm.c
+++ b/drivers/iommu/intel-svm.c
@@ -586,14 +586,15 @@ static irqreturn_t prq_event_thread(int irq, void *d)
* any faults on kernel addresses. */
if (!svm->mm)
goto bad_req;
- /* If the mm is already defunct, don't handle faults. */
- if (!mmget_not_zero(svm->mm))
- goto bad_req;

/* If address is not canonical, return invalid response */
if (!is_canonical_address(address))
goto bad_req;

+ /* If the mm is already defunct, don't handle faults. */
+ if (!mmget_not_zero(svm->mm))
+ goto bad_req;
+
down_read(&svm->mm->mmap_sem);
vma = find_extend_vma(svm->mm, address);
if (!vma || address < vma->vm_start)