Re: [RESEND PATCH v8 00/11] Fix BUG_ON in vfio_iommu_group_notifier()

[Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>]

On Mon, May 02, 2022 at 12:12:04PM -0400, Qian Cai wrote:
> On Mon, Apr 18, 2022 at 08:49:49AM +0800, Lu Baolu wrote:
> > Hi Joerg,
> > 
> > This is a resend version of v8 posted here:
> > https://lore.kernel.org/linux-iommu/20220308054421.847385-1-baolu.lu@linux.intel.com/
> > as we discussed in this thread:
> > https://lore.kernel.org/linux-iommu/Yk%2Fq1BGN8pC5HVZp@8bytes.org/
> > 
> > All patches can be applied perfectly except this one:
> >  - [PATCH v8 02/11] driver core: Add dma_cleanup callback in bus_type
> > It conflicts with below refactoring commit:
> >  - 4b775aaf1ea99 "driver core: Refactor sysfs and drv/bus remove hooks"
> > The conflict has been fixed in this post.
> > 
> > No functional changes in this series. I suppress cc-ing this series to
> > all v8 reviewers in order to avoid spam.
> > 
> > Please consider it for your iommu tree.
> 
> Reverting this series fixed an user-after-free while doing SR-IOV.
> 
>  BUG: KASAN: use-after-free in __lock_acquire
>  Read of size 8 at addr ffff080279825d78 by task qemu-system-aar/22429
>  CPU: 24 PID: 22429 Comm: qemu-system-aar Not tainted 5.18.0-rc5-next-20220502 #69
>  Call trace:
>   dump_backtrace
>   show_stack
>   dump_stack_lvl
>   print_address_description.constprop.0
>   print_report
>   kasan_report
>   __asan_report_load8_noabort
>   __lock_acquire
>   lock_acquire.part.0
>   lock_acquire
>   _raw_spin_lock_irqsave
>   arm_smmu_detach_dev
>   arm_smmu_detach_dev at drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c:2377
>   arm_smmu_attach_dev

Hum.

So what has happened is that VFIO does this sequence:

 iommu_detach_group()
 iommu_domain_free()
 iommu_group_release_dma_owner()

Which, I think should be valid, API wise.

From what I can see reading the code SMMUv3 blows up above because it
doesn't have a detach_dev op:

	.default_domain_ops = &(const struct iommu_domain_ops) {
		.attach_dev		= arm_smmu_attach_dev,
		.map_pages		= arm_smmu_map_pages,
		.unmap_pages		= arm_smmu_unmap_pages,
		.flush_iotlb_all	= arm_smmu_flush_iotlb_all,
		.iotlb_sync		= arm_smmu_iotlb_sync,
		.iova_to_phys		= arm_smmu_iova_to_phys,
		.enable_nesting		= arm_smmu_enable_nesting,
		.free			= arm_smmu_domain_free,
	}

But it is internally tracking the domain inside the master - so when
the next domain is attached it does this:

static void arm_smmu_detach_dev(struct arm_smmu_master *master)
{
	struct arm_smmu_domain *smmu_domain = master->domain;

	spin_lock_irqsave(&smmu_domain->devices_lock, flags);

And explodes as the domain has been freed but master->domain was not
NULL'd.

It worked before because iommu_detach_group() used to attach the
default group and that was before the domain was freed in the above
sequence.

I'm guessing SMMU3 needs to call it's arm_smmu_detach_dev(master) from
the detach_dev op and null it's cached copy of the domain, but I don't
know this driver.. Robin?

Thanks,
Jason
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