linux-kernel - RE: [RFC PATCH] iommufd: Destroy vdevice on device unbind

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <BN9PR11MB5276BB7E4927EA06B5B85AE58C7DA@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Thu, 19 Jun 2025 05:37:33 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Aneesh Kumar K.V <aneesh.kumar@...nel.org>
CC: "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Joerg Roedel
	<joro@...tes.org>, Will Deacon <will@...nel.org>, Robin Murphy
	<robin.murphy@....com>
Subject: RE: [RFC PATCH] iommufd: Destroy vdevice on device unbind

> From: Jason Gunthorpe <jgg@...pe.ca>
> Sent: Wednesday, June 18, 2025 11:00 PM
> 
> On Wed, Jun 18, 2025 at 08:22:44PM +0530, Aneesh Kumar K.V wrote:
> > > The full sequence I would expect a sane userspace to do is:
> > >
> > > open(vfio_cdev)
> > > ioctl(vfio_cdev, VFIO_DEVICE_BIND_IOMMUFD, iommufd)
> > > ioctl(iommufd, IOMMUFD_CMD_VIOMMU_ALLOC)
> > > ioctl(iommufd, IOMMUFD_CMD_VDEVICE_ALLOC)
> > > ioctl(iommufd, IOMMUFD_CMD_VDEVICE_DEALLOC)
> > > ioctl(iommufd, IOMMUFD_CMD_VIOMMU_DEALLOC)
> > > close(vfio_cdev);
> > >
> >
> > And if the user does
> >
> > open(vfio_cdev)
> > ioctl(vfio_cdev, VFIO_DEVICE_BIND_IOMMUFD, iommufd)
> > ioctl(iommufd, IOMMUFD_CMD_VIOMMU_ALLOC)
> > ioctl(iommufd, IOMMUFD_CMD_VDEVICE_ALLOC)
> > close(vfio_cdev);   -> this should call vdevice_destroy because idevice is
> getting destroyed here (we will put XA_ZERO_ENTRY here).
> 
> Yes, we have to destroy the vdevice internally here
> 
> > ioctl(iommufd, IOMMUFD_CMD_VDEVICE_DEALLOC) -> No error, we
> convert the XA_ZERO_ENTRY to NULL here?
> 
> This should probably fail since the user has done something wrong and
> it would be the only way to realize it. The failure could clean up the
> tombstone, or it could just leak I don't have a strong feeling.
> 
> If you leak then using XA_ZERO_ENTRY is easy, if you want to clean up
> then you'd have to have a global static 'tombstone object' that sits
> in the xarray.
> 

I prefer to leaking as it's simpler. The only value of cleanup is to get
one free object ID, which matters little upon a failure condition.