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

zhangfei.gao
2022-04-15T10:14:30Z

On 2022/4/15 下午5:51, Fenghua Yu wrote:
> 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;
This patch can not be applied on 5.18-rc2 for intel part.
It should work for arm.

In fact I have a similar patch at hand but pending since I found an issue.

I start & stop nginx via this cmd.
//start
sudo sbin/nginx                    // this alloc an ioasid=1
//stop
sudo sbin/nginx -s quit    // this does not free ioasid=1, but still
alloc ioasid=2.
So ioasid will keep allocated but not freed if continue start/stop
nginx,  though not impact the nginx function.

stop nginx with -s quit still calls
src/core/nginx.c
main -> ngx_ssl_init -> openssl engine:    bind_fn -> ... -> alloc asid
But openssl engine: ENGINE_free is not called

Still in checking nginx code.

Or do you test with nginx?

Thanks