Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit

Fenghua Yu
2022-04-15T09:50:47Z

On Thu, Apr 14, 2022 at 06:08:09PM +0800, zhangfei.gao@foxmail.com wrote:
>
> On 2022/4/12 下午11:35, zhangfei.gao@foxmail.com wrote:
> > Hi, Fenghua
> >
> > On 2022/4/12 下午9:41, Fenghua Yu wrote:
> > > Hi, Zhangfei,
> > >
> > > On Tue, Apr 12, 2022 at 03:04:09PM +0800, zhangfei.gao@foxmail.com
> > > wrote:
> > > >
> > > > On 2022/4/11 下午10:52, Dave Hansen wrote:
> > > > > On 4/11/22 07:44, zhangfei.gao@foxmail.com wrote:
> > > > > > On 2022/4/11 下午10:36, Dave Hansen wrote:
> > > > > > > On 4/11/22 07:20, zhangfei.gao@foxmail.com wrote:
> > Agree with Dave, I think user space should not be broken.
> >
> > Thanks
>
> Any plan about this regression?
> Currently I need this patch to workaround the issue.
>
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> index 22ddd05bbdcd..2d74ac53d11c 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
> @@ -4,6 +4,7 @@
>   */
>
>  #include <linux/mm.h>
> +#include <linux/sched/mm.h>
>  #include <linux/mmu_context.h>
>  #include <linux/mmu_notifier.h>
>  #include <linux/slab.h>
> @@ -363,6 +364,7 @@ arm_smmu_sva_bind(struct device *dev, struct mm_struct
> *mm, void *drvdata)
>
>         mutex_lock(&sva_lock);
>         handle = __arm_smmu_sva_bind(dev, mm);
> +       mmget(mm);
>         mutex_unlock(&sva_lock);
>         return handle;
>  }
> @@ -377,6 +379,7 @@ void arm_smmu_sva_unbind(struct iommu_sva *handle)
>                 arm_smmu_mmu_notifier_put(bond->smmu_mn);
>                 kfree(bond);
>         }
> +       mmput(bond->mm);
>         mutex_unlock(&sva_lock);
>  }

Could you please review and/or test this patch? It's supposed to fix
the PASID issue on both ARM and X86.

From a6444e1e5bd8076f5e5c5e950d3192de327f0c9c Mon Sep 17 00:00:00 2001
From: Fenghua Yu <fenghua.yu@intel.com>
Date: Fri, 15 Apr 2022 00:51:33 -0700
Subject: [RFC PATCH] iommu/sva: Fix PASID use-after-free issue

A PASID might be still used even though it is freed on mm exit.

process A:
sva_bind();
ioasid_alloc() = N; // Get PASID N for the mm
fork(): // spawn process B
exit();
ioasid_free(N);

process B:
device uses PASID N -> failure
sva_unbind();

Dave Hansen suggests to take a refcount on the mm whenever binding the
PASID to a device and drop the refcount on unbinding. The mm won't be
dropped if the PASID is still bound to it.

Fixes: 701fac40384f ("iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit")

Reported-by: Zhangfei Gao <zhangfei.gao@foxmail.com>
Suggested-by: Dave Hansen" <dave.hansen@linux.intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 6 ++++++
drivers/iommu/intel/svm.c | 4 ++++
2 files changed, 10 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
index 22ddd05bbdcd..3fcb842a0df0 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
@@ -7,6 +7,7 @@
#include <linux/mmu_context.h>
#include <linux/mmu_notifier.h>
#include <linux/slab.h>
+#include <linux/sched/mm.h>

#include "arm-smmu-v3.h"
#include "../../iommu-sva-lib.h"
@@ -363,6 +364,9 @@ arm_smmu_sva_bind(struct device *dev, struct mm_struct *mm, void *drvdata)

mutex_lock(&sva_lock);
handle = __arm_smmu_sva_bind(dev, mm);
+ /* Take an mm refcount on a successful bind. */
+ if (!IS_ERR(handle))
+ mmget(mm);
mutex_unlock(&sva_lock);
return handle;
}
@@ -372,6 +376,8 @@ void arm_smmu_sva_unbind(struct iommu_sva *handle)
struct arm_smmu_bond *bond = sva_to_bond(handle);

mutex_lock(&sva_lock);
+ /* Drop an mm refcount. */
+ mmput(bond->mm);
if (refcount_dec_and_test(&bond->refs)) {
list_del(&bond->list);
arm_smmu_mmu_notifier_put(bond->smmu_mn);
diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 23a38763c1d1..345a0d5d7922 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -403,6 +403,8 @@ static struct iommu_sva *intel_svm_bind_mm(struct intel_iommu *iommu,
goto free_sdev;

list_add_rcu(&sdev->list, &svm->devs);
+ /* Take an mm refcount on binding mm. */
+ mmget(mm);
success:
return &sdev->sva;

@@ -465,6 +467,8 @@ static int intel_svm_unbind_mm(struct device *dev, u32 pasid)
kfree(svm);
}
}
+ /* Drop an mm reference on unbinding mm. */
+ mmput(mm);
}
out:
return ret;
--
2.32.0