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

zhangfei.gao
2022-04-15T11:53:49Z

On 2022/4/15 下午6:50, Fenghua Yu wrote:
> Hi, Zhangfei,
>
> On Fri, Apr 15, 2022 at 06:14:09PM +0800, zhangfei.gao@foxmail.com wrote:
>>
>> 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:
>>> 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.
> What error do you see? Could you please send to me errors?
>
> I download this patch from:
> https://lore.kernel.org/lkml/YllADL6uMoLllzQo@fyu1.sc.intel.com/raw
> git am to either v5.18-rc2 or the latest upstream without any issue.
It is my copy paste issue.

I have tested, nginx woks well.

Other than the following issue,
Each time /sbin/nginx will alloc ioasid but not free.
which I think it maybe nginx issue or the mis-usage, will ask there.

Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>

>
>> 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?
> On my X86 machine, nginx doesn't trigger the kernel sva binding function
> to allocate ioasid. I tried pre- nstalled nginx/openssl and also tried my built
> a few versions of nginx/openssl. nginx does call OPENSSL_init_ssl() but
> doesn't go to the binding function. Don't know if it's my configuration issue.
> Maybe you can give me some advice?
I am using openssl engine, which use crypto driver and using sva via uacce.
nginx -> openssl -> openssl engine -> sva related.

>
> I test the patch with a few internal test tools and observe mmget()/mmput()
> works fine in various cases.
OK, thanks