linux-kernel - Re: [RFC PATCH] iommu/vt-d: Add sanity check to iommu_sva_bind

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Message-ID: <89029bfb-bdf6-43e3-b24c-09c266277f0e@linux.intel.com>
Date:   Fri, 14 Oct 2022 09:52:44 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jerry Snitselaar <jsnitsel@...hat.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [RFC PATCH] iommu/vt-d: Add sanity check to
 iommu_sva_bind_device()

On 2022/10/13 23:33, 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@...tes.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Lu Baolu <baolu.lu@...ux.intel.com>
> Signed-off-by: Jerry Snitselaar <jsnitsel@...hat.com>
> ---
> 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);
> +	}

If that's the case, dev_iommu_ops() will warn a NULL pointer reference.
This kind of error will be discovered at the first place.

Best regards,
baolu

> +
> +	ops = dev_iommu_ops(dev);
>   
>   	if (!ops->sva_bind)
>   		return ERR_PTR(-ENODEV);