Re: [PATCH 3/4] vfio: Follow a strict lifetime for struct iommu_group *

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 9/8/22 2:45 PM, Jason Gunthorpe wrote:
> The iommu_group comes from the struct device that a driver has been bound
> to and then created a struct vfio_device against. To keep the iommu layer
> sane we want to have a simple rule that only an attached driver should be
> using the iommu API. Particularly only an attached driver should hold
> ownership.
> 
> In VFIO's case since it uses the group APIs and it shares between
> different drivers it is a bit more complicated, but the principle still
> holds.
> 
> Solve this by waiting for all users of the vfio_group to stop before
> allowing vfio_unregister_group_dev() to complete. This is done with a new
> completion to know when the users go away and an additional refcount to
> keep track of how many device drivers are sharing the vfio group. The last
> driver to be unregistered will clean up the group.
> 
> This solves crashes in the S390 iommu driver that come because VFIO ends
> up racing releasing ownership (which attaches the default iommu_domain to
> the device) with the removal of that same device from the iommu
> driver. This is a side case that iommu drivers should not have to cope
> with.
> 
>    iommu driver failed to attach the default/blocking domain
>    WARNING: CPU: 0 PID: 5082 at drivers/iommu/iommu.c:1961 iommu_detach_group+0x6c/0x80
>    Modules linked in: macvtap macvlan tap vfio_pci vfio_pci_core irqbypass vfio_virqfd kvm nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set nf_tables nfnetlink mlx5_ib sunrpc ib_uverbs ism smc uvdevice ib_core s390_trng eadm_sch tape_3590 tape tape_class vfio_ccw mdev vfio_iommu_type1 vfio zcrypt_cex4 sch_fq_codel configfs ghash_s390 prng chacha_s390 libchacha aes_s390 mlx5_core des_s390 libdes sha3_512_s390 nvme sha3_256_s390 sha512_s390 sha256_s390 sha1_s390 sha_common nvme_core zfcp scsi_transport_fc pkey zcrypt rng_core autofs4
>    CPU: 0 PID: 5082 Comm: qemu-system-s39 Tainted: G        W          6.0.0-rc3 #5
>    Hardware name: IBM 3931 A01 782 (LPAR)
>    Krnl PSW : 0704c00180000000 000000095bb10d28 (iommu_detach_group+0x70/0x80)
>               R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
>    Krnl GPRS: 0000000000000001 0000000900000027 0000000000000039 000000095c97ffe0
>               00000000fffeffff 00000009fc290000 00000000af1fda50 00000000af590b58
>               00000000af1fdaf0 0000000135c7a320 0000000135e52258 0000000135e52200
>               00000000a29e8000 00000000af590b40 000000095bb10d24 0000038004b13c98
>    Krnl Code: 000000095bb10d18: c020003d56fc        larl    %r2,000000095c2bbb10
>                           000000095bb10d1e: c0e50019d901        brasl   %r14,000000095be4bf20
>                          #000000095bb10d24: af000000            mc      0,0
>                          >000000095bb10d28: b904002a            lgr     %r2,%r10
>                           000000095bb10d2c: ebaff0a00004        lmg     %r10,%r15,160(%r15)
>                           000000095bb10d32: c0f4001aa867        brcl    15,000000095be65e00
>                           000000095bb10d38: c004002168e0        brcl    0,000000095bf3def8
>                           000000095bb10d3e: eb6ff0480024        stmg    %r6,%r15,72(%r15)
>    Call Trace:
>     [<000000095bb10d28>] iommu_detach_group+0x70/0x80
>    ([<000000095bb10d24>] iommu_detach_group+0x6c/0x80)
>     [<000003ff80243b0e>] vfio_iommu_type1_detach_group+0x136/0x6c8 [vfio_iommu_type1]
>     [<000003ff80137780>] __vfio_group_unset_container+0x58/0x158 [vfio]
>     [<000003ff80138a16>] vfio_group_fops_unl_ioctl+0x1b6/0x210 [vfio]
>    pci 0004:00:00.0: Removing from iommu group 4
>     [<000000095b5b62e8>] __s390x_sys_ioctl+0xc0/0x100
>     [<000000095be5d3b4>] __do_syscall+0x1d4/0x200
>     [<000000095be6c072>] system_call+0x82/0xb0
>    Last Breaking-Event-Address:
>     [<000000095be4bf80>] __warn_printk+0x60/0x68
> 
> It reflects that domain->ops->attach_dev() failed because the driver has
> already passed the point of destructing the device.
> 
> Fixes: 9ac8545199a1 ("iommu: Fix use-after-free in iommu_release_device")
> Reported-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

I've been running with only the first 3 patches in this series (the vfio changes) and can confirm that they resolve the reported issue for me.

Tested-by: Matthew Rosato <mjrosato@linux.ibm.com> # s390

...

> +static void vfio_group_remove(struct vfio_group *group)
> +{
> +	/* Pairs with vfio_create_group() */

Nit: vfio_create_group() no longer exists as of patch 1