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

Jason Gunthorpe
2022-05-02T16:42:25Z

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