Re: [PATCH v2] iommu/arm-smmu: Fix arm_smmu_device refcount leak in address translation

From: Rob Clark <robdclark@chromium.org>
To: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Cc: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Will Deacon <will@kernel.org>, Joerg Roedel <joro@8bytes.org>,
	yuanxzhang@fudan.edu.cn, iommu@lists.linux-foundation.org,
	Jordan Crouse <jordan@cosmicpenguin.net>,
	Xin Tan <tanxin.ctf@gmail.com>, Jon Hunter <jonathanh@nvidia.com>,
	Robin Murphy <robin.murphy@arm.com>,
	"moderated list:ARM64 PORT \(AARCH64 ARCHITECTURE\)"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2] iommu/arm-smmu: Fix arm_smmu_device refcount leak in address translation
Date: Thu, 10 Jun 2021 15:28:15 -0700	[thread overview]
Message-ID: <CAJs_Fx6qgQFOp16SLQfz-Aaj4mqTo+vCvfpQr_E3UapVTrsu6Q@mail.gmail.com> (raw)
In-Reply-To: <1623293391-17261-1-git-send-email-xiyuyang19@fudan.edu.cn>

On Wed, Jun 9, 2021 at 7:50 PM Xiyu Yang <xiyuyang19@fudan.edu.cn> wrote:
>
> The reference counting issue happens in several exception handling paths
> of arm_smmu_iova_to_phys_hard(). When those error scenarios occur, the
> function forgets to decrease the refcount of "smmu" increased by
> arm_smmu_rpm_get(), causing a refcount leak.
>
> Fix this issue by jumping to "out" label when those error scenarios
> occur.
>
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
> ---
>  drivers/iommu/arm/arm-smmu/arm-smmu.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> index 6f72c4d208ca..3a3847277320 100644
> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> @@ -1271,6 +1271,7 @@ static phys_addr_t arm_smmu_iova_to_phys_hard(struct iommu_domain *domain,
>         u64 phys;
>         unsigned long va, flags;
>         int ret, idx = cfg->cbndx;
> +       phys_addr_t addr = 0;
>
>         ret = arm_smmu_rpm_get(smmu);
>         if (ret < 0)
> @@ -1290,6 +1291,7 @@ static phys_addr_t arm_smmu_iova_to_phys_hard(struct iommu_domain *domain,
>                 dev_err(dev,
>                         "iova to phys timed out on %pad. Falling back to software table walk.\n",
>                         &iova);
> +               arm_smmu_rpm_put(smmu);
>                 return ops->iova_to_phys(ops, iova);

I suppose you could also:

   addr = ops->iov_to_phys(...);
   goto out;

but either way,

Reviewed-by: Rob Clark <robdclark@chromium.org>

>         }
>
> @@ -1298,12 +1300,14 @@ static phys_addr_t arm_smmu_iova_to_phys_hard(struct iommu_domain *domain,
>         if (phys & ARM_SMMU_CB_PAR_F) {
>                 dev_err(dev, "translation fault!\n");
>                 dev_err(dev, "PAR = 0x%llx\n", phys);
> -               return 0;
> +               goto out;
>         }
>
> +       addr = (phys & GENMASK_ULL(39, 12)) | (iova & 0xfff);
> +out:
>         arm_smmu_rpm_put(smmu);
>
> -       return (phys & GENMASK_ULL(39, 12)) | (iova & 0xfff);
> +       return addr;
>  }
>
>  static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
> --
> 2.7.4
>

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