linux-kernel - Re: [PATCH RESEND STABLE v6.1] iommu: Avoid races around default domain allocations

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Date: Tue, 5 Mar 2024 13:01:12 +0530
From: Nikhil V <quic_nprakash@...cinc.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: Charan Teja Kalla <quic_charante@...cinc.com>,
        Joerg Roedel
	<joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy
	<robin.murphy@....com>, <linux-kernel@...r.kernel.org>,
        <iommu@...ts.linux.dev>, <stable@...r.kernel.org>
Subject: Re: [PATCH RESEND STABLE v6.1] iommu: Avoid races around default
 domain allocations



On 3/4/2024 6:55 PM, Greg KH wrote:
> On Mon, Mar 04, 2024 at 04:40:50PM +0530, Nikhil V wrote:
>> From: Charan Teja Kalla <quic_charante@...cinc.com>
>>
>> This fix is applicable for LTS kernel, 6.1.y. In latest kernels, this race
>> issue is fixed by the patch series [1] and [2]. The right thing to do here
>> would have been propagating these changes from latest kernel to the stable
>> branch, 6.1.y. However, these changes seems too intrusive to be picked for
>> stable branches. Hence, the fix proposed can be taken as an alternative
>> instead of backporting the patch series.
>> [1] https://lore.kernel.org/all/0-v8-81230027b2fa+9d-iommu_all_defdom_jgg@nvidia.com/
>> [2] https://lore.kernel.org/all/0-v5-1b99ae392328+44574-iommu_err_unwind_jgg@nvidia.com/
>>
>> Issue:
>> A race condition is observed when arm_smmu_device_probe and
>> modprobe of client devices happens in parallel. This results
>> in the allocation of a new default domain for the iommu group
>> even though it was previously allocated and the respective iova
>> domain(iovad) was initialized. However, for this newly allocated
>> default domain, iovad will not be initialized. As a result, for
>> devices requesting dma allocations, this uninitialized iovad will
>> be used, thereby causing NULL pointer dereference issue.
>>
>> Flow:
>> - During arm_smmu_device_probe, bus_iommu_probe() will be called
>> as part of iommu_device_register(). This results in the device probe,
>> __iommu_probe_device().
>>
>> - When the modprobe of the client device happens in parallel, it
>> sets up the DMA configuration for the device using of_dma_configure_id(),
>> which inturn calls iommu_probe_device(). Later, default domain is
>> allocated and attached using iommu_alloc_default_domain() and
>> __iommu_attach_device() respectively. It then ends up initializing a
>> mapping domain(IOVA domain) and rcaches for the device via
>> arch_setup_dma_ops()->iommu_setup_dma_ops().
>>
>> - Now, in the bus_iommu_probe() path, it again tries to allocate
>> a default domain via probe_alloc_default_domain(). This results in
>> allocating a new default domain(along with IOVA domain) via
>> __iommu_domain_alloc(). However, this newly allocated IOVA domain
>> will not be initialized.
>>
>> - Now, when the same client device tries dma allocations via
>> iommu_dma_alloc(), it ends up accessing the rcaches of the newly
>> allocated IOVA domain, which is not initialized. This results
>> into NULL pointer dereferencing.
>>
>> Fix this issue by adding a check in probe_alloc_default_domain()
>> to see if the iommu_group already has a default domain allocated
>> and initialized.
>>
>> Cc: <stable@...r.kernel.org> # see patch description, fix applicable only for 6.1.y
>> Signed-off-by: Charan Teja Kalla <quic_charante@...cinc.com>
>> Co-developed-by: Nikhil V <quic_nprakash@...cinc.com>
>> Signed-off-by: Nikhil V <quic_nprakash@...cinc.com>
>> ---
>>   drivers/iommu/iommu.c | 3 +++
>>   1 file changed, 3 insertions(+)
> 
> Why RESEND?  What happened to the first send?
> 
> thanks,
> 
> greg k-h


Hi Greg,

There are no changes as such w.r.t first send, [1]. It is resent to gain 
attention on this patch. Also, we have added a proper Cc: stable tag 
with this patch.


[1] 
https://lore.kernel.org/all/cbf1295589bd90083ad6f75a7fbced01f327c047.1708680521.git.quic_nprakash@quicinc.com/

Thanks
Nikhil V