linux-kernel - Re: [PATCH V1 1/1] iommu: Make sure device's ID array elements are unique

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Date:   Wed, 20 Dec 2017 11:28:29 +0100
From:   Tomasz Nowicki <tn@...ihalf.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Tomasz Nowicki <tomasz.nowicki@...iumnetworks.com>
Cc:     joro@...tes.org, robin.murphy@....com, will.deacon@....com,
        lorenzo.pieralisi@....com, bhelgaas@...gle.com,
        Jayachandran.Nair@...ium.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-acpi@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Ganapatrao.Kulkarni@...ium.com, mw@...ihalf.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH V1 1/1] iommu: Make sure device's ID array elements are
 unique

On 19.12.2017 17:37, Alex Williamson wrote:
> On Tue, 19 Dec 2017 16:20:21 +0100
> Tomasz Nowicki <tomasz.nowicki@...iumnetworks.com> wrote:
> 
>> While iterating over DMA aliases for a PCI device, for some rare cases
>> (i.e. PCIe-to-PCI/X bridges) we may get exactly the same ID as initial child
>> device. In turn, the same ID may get registered for a device multiple times.
>> Eventually IOMMU  driver may try to configure the same ID within domain
>> multiple times too which for some IOMMU drivers is illegal and causes kernel
>> panic.
>>
>> Rule out ID duplication prior to device ID array registration.
>>
>> CC: stable@...r.kernel.org	# v4.14+
> 
> You've identified a release, is there a specific commit this fixes?

Yes, it was triggered by converting drm_pci_init() to 
pci_register_driver() in ast_drv.c

Fixes: 10631d724def ("drm/pci: Deprecate drm_pci_init/exit completely
")

> 
>> Signed-off-by: Tomasz Nowicki <tomasz.nowicki@...iumnetworks.com>
>> ---
>>   drivers/iommu/iommu.c | 28 ++++++++++++++++++++++++++++
>>   1 file changed, 28 insertions(+)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 3de5c0b..9b2c138 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -1945,6 +1945,31 @@ void iommu_fwspec_free(struct device *dev)
>>   }
>>   EXPORT_SYMBOL_GPL(iommu_fwspec_free);
>>   
>> +static void iommu_fwspec_remove_ids_dup(struct device *dev, u32 *ids,
>> +					int *num_ids)
>> +{
>> +	struct iommu_fwspec *fwspec = dev->iommu_fwspec;
>> +	int i, j, k, valid_ids = *num_ids;
>> +
>> +	for (i = 0; i < valid_ids; i++) {
>> +		for (j = 0; j < fwspec->num_ids; j++) {
>> +			if (ids[i] != fwspec->ids[j])
>> +				continue;
>> +
>> +			dev_info(dev, "found 0x%x ID duplication, skipped\n",
>> +				 ids[i]);
>> +
>> +			for (k = i + 1; k < valid_ids; k++)
>> +				ids[k - 1] = ids[k];
> 
> Use memmove()?

Right.

> 
>> +
>> +			valid_ids--;
>> +			break;
> 
> At this point ids[i] is not the ids[i] that we tested for dupes, it's
> what was ids[i + 1], but we're going to i++ on the next iteration and
> we therefore never test that entry.

Good point.

Now the fundamental question is where we should put the patch, here or 
in SMMUv3 driver as per Robin suggestion.

Thanks,
Tomasz