linux-kernel - RE: [PATCH v3 09/17] iommufd: Add IOMMU_HWPT

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Message-ID: <DS0PR11MB7529EA8256BD06A96C8D1A85C308A@DS0PR11MB7529.namprd11.prod.outlook.com>
Date:   Thu, 3 Aug 2023 03:07:23 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
Subject: RE: [PATCH v3 09/17] iommufd: Add IOMMU_HWPT_INVALIDATE

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Thursday, August 3, 2023 10:17 AM
> 
> On Mon, Jul 31, 2023 at 10:19:09AM -0300, Jason Gunthorpe wrote:
> > On Mon, Jul 31, 2023 at 10:07:32AM +0000, Liu, Yi L wrote:
> > > > > +		goto out_put_hwpt;
> > > > > +	}
> > > > > +
> > > > > +	/*
> > > > > +	 * Copy the needed fields before reusing the ucmd buffer, this
> > > > > +	 * avoids memory allocation in this path.
> > > > > +	 */
> > > > > +	user_ptr = cmd->data_uptr;
> > > > > +	user_data_len = cmd->data_len;
> > > >
> > > > Uhh, who checks that klen < the temporary stack struct?
> > >
> > > Take vtd as an example. The invalidate structure is struct
> iommu_hwpt_vtd_s1_invalidate[1].
> > > The klen is sizeof(struct iommu_hwpt_vtd_s1_invalidate)[2].
> iommu_hwpt_vtd_s1_invalidate
> > > is also placed in the temporary stack struct (actually it is a union)[1]. So the klen
> should
> > > be <= temporary stack.
> >
> > Ohh, I think I would add a few comments noting that the invalidate
> > structs need to be added to that union. Easy to miss.
> 
> Added here:
> 
> -        * Copy the needed fields before reusing the ucmd buffer, this
> -        * avoids memory allocation in this path.
> +        * Copy the needed fields before reusing the ucmd buffer, this avoids
> +        * memory allocation in this path. Again, user invalidate data struct
> +        * must be added to the union ucmd_buffer.
> 
> > > It's not so explicit though. Perhaps worth to have a check like below in this patch?
> > >
> > > if (unlikely(klen > sizeof(union ucmd_buffer)))
> > > 	return -EINVAL;
> >
> > Yes, stick this in the domain allocate path with a WARN_ON. The driver
> > is broken to allocate a domain with an invalid size.
> 
> And here too with a WARN_ON_ONCE.
> 
> +       /*
> +        * Either the driver is broken by having an invalid size, or the user
> +        * invalidate data struct used by the driver is missing in the union.
> +        */
> +       if (WARN_ON_ONCE(hwpt->domain->ops->cache_invalidate_user &&
> +                        (!hwpt->domain->ops->cache_invalidate_user_data_len ||
> +                         hwpt->domain->ops->cache_invalidate_user_data_len >
> +                         sizeof(union ucmd_buffer)))) {
> +               rc = -EINVAL;
> +               goto out_abort;
> +
> +       }
> 
> Though I am making this cache_invalidate_user optional here, I
> wonder if there actually could be a case that a user-managed
> domain doesn't need a cache_invalidate_user op...

If user-managed domain is the stage-1 domain in nested, then seems not
possible as cache invalidate is a must. But I think this logic is fine as not
all the domains allocated by the user is user-managed. It may be kernel
managed like the s2 domains.

Regards,
Yi Liu