Re: [PATCH v2] vfio: Follow a strict lifetime for struct iommu_group

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 26 Sep 2022 13:03:56 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:

> On 9/22/22 8:06 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 indicates 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>
> > Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
> > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> > ---
> >  drivers/vfio/vfio.h      |  8 +++++
> >  drivers/vfio/vfio_main.c | 68 ++++++++++++++++++++++++++--------------
> >  2 files changed, 53 insertions(+), 23 deletions(-)
> > 
> > v2
> >  - Rebase on the vfio struct device series and the container.c series
> >  - Drop patches 1 & 2, we need to have working error unwind, so another
> >    test is not a problem
> >  - Fold iommu_group_remove_device() into vfio_device_remove_group() so
> >    that it forms a strict pairing with the two allocation functions.
> >  - Drop the iommu patch from the series, it needs more work and discussion
> > v1 https://lore.kernel.org/r/0-v1-ef00ffecea52+2cb-iommu_group_lifetime_jgg@nvidia.com
> > 
> > This could probably use another quick sanity test due to all the rebasing,
> > Alex if you are happy let's wait for Matthew.
> >   
> 
> I have been re-running the same series of tests on this version (on top of vfio-next) and this still resolves the reported issue.  Thanks Jason!

Thanks all.  Applied to vfio next branch for v6.1.  Thanks,

Alex