Messages in this thread |  | | Date | Tue, 3 May 2022 14:04:37 +0100 | Subject | Re: [RESEND PATCH v8 00/11] Fix BUG_ON in vfio_iommu_group_notifier() | From | Robin Murphy <> |
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On 2022-05-02 17:42, Jason Gunthorpe wrote: > 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.
Oof, I totally overlooked the significance of that little subtlety in review :(
> 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?
The original intent was that .detach_dev is deprecated in favour of default domains, and when the latter are in use, a device is always attached *somewhere* once probed (i.e. group->domain is never NULL). At face value, the neatest fix IMO would probably be for SMMUv3's .domain_free to handle smmu_domain->devices being non-empty and detach them at that point. However that wouldn't be viable for virtio-iommu or anyone else keeping an internal one-way association of devices to their current domains.
If we're giving up entirely on that notion of .detach_dev going away then all default-domain-supporting drivers probably want checking to make sure that path hasn't bitrotted; both Arm SMMU drivers had it proactively removed 6 years ago; virtio-iommu never had it at all; newer drivers like apple-dart have some code there, but it won't have ever run until now.
We *could* stay true to the original paradigm by introducing some real usage of IOMMU_DOMAIN_BLOCKED, such that we could keep one or more of those around to actively attach to instead of having groups in this unattached limbo state, but that's a bigger job involving adding support to drivers as well; too much for a quick fix now...
Robin.
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