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

[Fenghua Yu]

Hi, Zhangfei,

On Fri, Apr 15, 2022 at 06:14:09PM +0800, zhangfei.gao@xxxxxxxxxxx wrote:
> 
> 
> On 2022/4/15 下午5:51, Fenghua Yu wrote:
> > On Thu, Apr 14, 2022 at 06:08:09PM +0800, zhangfei.gao@xxxxxxxxxxx wrote:
> > > On 2022/4/12 下午11:35, zhangfei.gao@xxxxxxxxxxx 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@xxxxxxxxx>
> > 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@xxxxxxxxxxx>
> > Suggested-by: Dave Hansen" <dave.hansen@xxxxxxxxxxxxxxx>
> > Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> > ---
> >   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@xxxxxxxxxxxxxxxxx/raw
git am to either v5.18-rc2 or the latest upstream without any issue.

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

Thanks.

-Fenghua