Messages in this thread Patch in this message | | | Date | Mon, 25 Apr 2022 21:20:36 -0700 | From | Fenghua Yu <> | Subject | Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit |
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Hi, Jean and Zhangfei,
On Mon, Apr 25, 2022 at 05:13:02PM +0100, Jean-Philippe Brucker wrote: > Could we move mm_pasid_drop() to __mmdrop() instead of __mmput()? For Arm > we do need to hold the mm_count until unbind(), and mmgrab()/mmdrop() is > also part of Lu's rework [1].
Is this a right fix for the issue? Could you please test it on ARM? I don't have an ARM machine.
Thanks.
-Fenghua
From 84aa68f6174439d863c40cdc2db0e1b89d620dd0 Mon Sep 17 00:00:00 2001 From: Fenghua Yu <fenghua.yu@intel.com> Date: Fri, 15 Apr 2022 00:51:33 -0700 Subject: [PATCH] iommu/sva: Fix PASID use-after-free issue
A PASID might be still used on ARM after it is freed in __mmput().
process: open()->sva_bind()->ioasid_alloc() = N; // Get PASID N for the mm exit(); exit_mm()->__mmput()->mm_pasid_drop()->mm->pasid = -1; // PASID -1 exit_files()->release(dev)->sva_unbind()->use mm->pasid; // Failure
To avoid the use-after-free issue, free the PASID after no device uses it, i.e. after all devices are unbound from the mm.
sva_bind()/sva_unbind() call mmgrab()/mmdrop() to track mm->mm_count. __mmdrop() is called only after mm->mm_count is zero. So freeing the PASID in __mmdrop() guarantees the PASID is safely freed only after no device is bound to the mm.
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: Jean-Philippe Brucker <jean-philippe@linaro.org> Suggested-by: Jacob Pan <jacob.jun.pan@linux.intel.com> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> --- kernel/fork.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 9796897560ab..35a3beff140b 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -792,6 +792,7 @@ void __mmdrop(struct mm_struct *mm) mmu_notifier_subscriptions_destroy(mm); check_mm(mm); put_user_ns(mm->user_ns); + mm_pasid_drop(mm); free_mm(mm); } EXPORT_SYMBOL_GPL(__mmdrop); @@ -1190,7 +1191,6 @@ static inline void __mmput(struct mm_struct *mm) } if (mm->binfmt) module_put(mm->binfmt->module); - mm_pasid_drop(mm); mmdrop(mm); } -- 2.32.0
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