On 2022/4/29 上午2:00, Fenghua Yu wrote:
> The PASID is being freed too early. It needs to stay around until after
> device drivers that might be using it have had a chance to clear it out
> of the hardware.
>
> As a reminder:
>
> mmget() /mmput() refcount the mm's address space
> mmgrab()/mmdrop() refcount the mm itself
>
> The PASID is currently tied to the life of the mm's address space and
> freed in __mmput(). This makes logical sense because the PASID can't be
> used once the address space is gone.
>
> But, this misses an important point: even after the address space is
> gone, the PASID will still be programmed into a device. Device drivers
> might, for instance, still need to flush operations that are outstanding
> and need to use that PASID. They do this at file->release() time.
>
> Device drivers call the IOMMU driver to hold a reference on the mm itself
> and drop it at file->release() time. But, the IOMMU driver holds a
> reference on the mm itself, not the address space. The address space
> (and the PASID) is long gone by the time the driver tries to clean up.
> This is effectively a use-after-free bug on the PASID.
>
> To fix this, move the PASID free operation from __mmput() to __mmdrop().
> This ensures that the IOMMU driver's existing mmgrab() keeps the PASID
> allocated until it drops its mm reference.
>
> Fixes: 701fac40384f ("iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit")
>
> Reported-by: Zhangfei Gao <[email protected]>
> Tested-by: Zhangfei Gao <[email protected]>
Tested-by: Zhangfei Gao <[email protected]>
Use the formal email, thanks
> Suggested-by: Jean-Philippe Brucker <[email protected]>
> Suggested-by: Jacob Pan <[email protected]>
> Reviewed-by: Jean-Philippe Brucker <[email protected]>
> Signed-off-by: Fenghua Yu <[email protected]>
> ---
>
> v2:
> - Dave Hansen rewrites the change log.
> - Add Tested-by: Zhangfei Gao <[email protected]>
> - Add Reviewed-by: Jean-Philippe Brucker <[email protected]>
>
> The original patch was posted and discussed in:
> https://lore.kernel.org/lkml/[email protected]/
>
> 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);
> }
>
On 2022/4/29 上午9:39, Zhangfei Gao wrote:
>
>
> On 2022/4/29 上午2:00, Fenghua Yu wrote:
>> The PASID is being freed too early. It needs to stay around until after
>> device drivers that might be using it have had a chance to clear it out
>> of the hardware.
>>
>> As a reminder:
>>
>> mmget() /mmput() refcount the mm's address space
>> mmgrab()/mmdrop() refcount the mm itself
>>
>> The PASID is currently tied to the life of the mm's address space and
>> freed in __mmput(). This makes logical sense because the PASID can't be
>> used once the address space is gone.
>>
>> But, this misses an important point: even after the address space is
>> gone, the PASID will still be programmed into a device. Device drivers
>> might, for instance, still need to flush operations that are outstanding
>> and need to use that PASID. They do this at file->release() time.
>>
>> Device drivers call the IOMMU driver to hold a reference on the mm
>> itself
>> and drop it at file->release() time. But, the IOMMU driver holds a
>> reference on the mm itself, not the address space. The address space
>> (and the PASID) is long gone by the time the driver tries to clean up.
>> This is effectively a use-after-free bug on the PASID.
>>
>> To fix this, move the PASID free operation from __mmput() to __mmdrop().
>> This ensures that the IOMMU driver's existing mmgrab() keeps the PASID
>> allocated until it drops its mm reference.
>>
>> Fixes: 701fac40384f ("iommu/sva: Assign a PASID to mm on PASID
>> allocation and free it on mm exit")
>>
>> Reported-by: Zhangfei Gao <[email protected]>
>> Tested-by: Zhangfei Gao <[email protected]>
>
> Tested-by: Zhangfei Gao <[email protected]>
>
> Use the formal email, thanks
>
>> Suggested-by: Jean-Philippe Brucker <[email protected]>
>> Suggested-by: Jacob Pan <[email protected]>
>> Reviewed-by: Jean-Philippe Brucker <[email protected]>
>> Signed-off-by: Fenghua Yu <[email protected]>
Hi,
Will this be taken for 5.18?
Thanks
>> ---
>>
>> v2:
>> - Dave Hansen rewrites the change log.
>> - Add Tested-by: Zhangfei Gao <[email protected]>
>> - Add Reviewed-by: Jean-Philippe Brucker <[email protected]>
>>
>> The original patch was posted and discussed in:
>> https://lore.kernel.org/lkml/[email protected]/
>>
>> 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);
>> }
>
On Fri, May 06 2022 at 09:49, Zhangfei Gao wrote:
> Will this be taken for 5.18?
It's queued in tip core/urgent and will go to Linus this week.