linux-kernel - Re: [PATCH v3 1/8] iommu: Add iopf domain attach/detach/replace interface

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Message-ID: <b0f5e418-8faa-45d1-b086-61f6c009c0cb@linux.intel.com>
Date: Wed, 21 Feb 2024 13:52:39 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...pe.ca>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Nicolin Chen <nicolinc@...dia.com>, "Liu, Yi L" <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Joel Granados <j.granados@...sung.com>
Cc: baolu.lu@...ux.intel.com, "iommu@...ts.linux.dev"
 <iommu@...ts.linux.dev>,
 "virtualization@...ts.linux-foundation.org"
 <virtualization@...ts.linux-foundation.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/8] iommu: Add iopf domain attach/detach/replace
 interface

On 2024/2/7 16:11, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Monday, January 22, 2024 3:39 PM
>>
>> There is a slight difference between iopf domains and non-iopf domains.
>> In the latter, references to domains occur between attach and detach;
>> While in the former, due to the existence of asynchronous iopf handling
>> paths, references to the domain may occur after detach, which leads to
>> potential UAF issues.
> 
> Does UAF still exist if iommu driver follows the guidance you just added
> to iopf_queue_remove_device()?
> 
> it clearly says that the driver needs to disable IOMMU PRI reception,
> remove device from iopf queue and disable PRI on the device.

The iopf_queue_remove_device() function is only called after the last
iopf-capable domain is detached from the device. It may not be called
during domain replacement. Hence, there is no guarantee that
iopf_queue_remove_device() will be called when a domain is detached from
the device.

> 
> presumably those are all about what needs to be done in the detach
> operation. Then once detach completes there should be no more
> reference to the domain from the iopf path?

The domain pointer stored in the iopf_group structure is only released
after the iopf response, possibly after the domain is detached from the
device. Thus, the domain pointer can only be freed after the iopf
response.

> 
>>
>> +struct iopf_attach_cookie {
>> +	struct iommu_domain *domain;
>> +	struct device *dev;
>> +	unsigned int pasid;
>> +	refcount_t users;
>> +
>> +	void *private;
>> +	void (*release)(struct iopf_attach_cookie *cookie);
>> +};
> 
> this cookie has nothing specific to iopf.
> 
> it may makes more sense to build a generic iommu_attach_device_cookie()
> helper so the same object can be reused in future other usages too.
> 
> within iommu core it can check domain iopf handler and this generic cookie
> to update iopf specific data e.g. the pasid_cookie xarray.

This means attaching an iopf-capable domain follows two steps:

1) Attaching the domain to the device.
2) Setting up the iopf data, necessary for handling iopf data.

This creates a time window during which the iopf is enabled, but the
software cannot handle it. Or not?

Best regards,
baolu