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Date:   Thu, 13 Oct 2022 08:37:30 -0700
From:   Jerry Snitselaar <jsnitsel@redhat.com>
To:     iommu@lists.linux.dev, linux-kernel@vger.kernel.org
Cc:     Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Lu Baolu <baolu.lu@linux.intel.com>
Subject: Re: [RFC PATCH] iommu/vt-d: Add sanity check to
 iommu_sva_bind_device()
Message-ID: <20221013153730.rwtukjgpdgwgfodv@cantor>
References: <20221013153355.2365865-1-jsnitsel@redhat.com>
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On Thu, Oct 13, 2022 at 08:33:55AM -0700, Jerry Snitselaar wrote:
> iommu_sva_bind_device() should only be called if
> iommu_dev_enable_feature() succeeded. There has been one case already
> where that hasn't been the case, which resulted in a null pointer
> deref in dev_iommu_ops(). To avoid that happening in the future if
> another driver makes that mistake, sanity check dev->iommu and
> dev->iommu->iommu_dev prior to calling dev_iommu_ops().
> 
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>
> ---

I don't know how many other drivers there will be in the future,
so quite possibly a non-issue. It did happen with the idxd driver
though, and I was thinking about that this morning so thought I
would send a patch to avoid it in the future.

Regards,
Jerry

> drivers/iommu/iommu.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 4893c2429ca5..20ec75667529 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2746,7 +2746,15 @@ iommu_sva_bind_device(struct device *dev, struct mm_struct *mm, void *drvdata)
>  {
>  	struct iommu_group *group;
>  	struct iommu_sva *handle = ERR_PTR(-EINVAL);
> -	const struct iommu_ops *ops = dev_iommu_ops(dev);
> +	const struct iommu_ops *ops;
> +
> +	if (!dev->iommu || !dev->iommu->iommu_dev) {
> +		dev_warn(dev, "%s called without checking succes of iommu_dev_enable_feature?\n",
> +			__func__);
> +		return ERR_PTR(-ENODEV);
> +	}
> +
> +	ops = dev_iommu_ops(dev);
>  
>  	if (!ops->sva_bind)
>  		return ERR_PTR(-ENODEV);
> -- 
> 2.37.2
>