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

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Message-ID: <DS0PR11MB75299A86DAD5030BC88C8CC3C308A@DS0PR11MB7529.namprd11.prod.outlook.com>
Date:   Thu, 3 Aug 2023 02:56:22 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     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>,
        "nicolinc@...dia.com" <nicolinc@...dia.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>,
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        <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: Jason Gunthorpe <jgg@...dia.com>
> Sent: Monday, July 31, 2023 9:19 PM
> 
> 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.

Sure. Actually, there are some description as below in patch [1]. Would
add some as well here.

"Cache invalidation path is performance path, so it's better to avoid
memory allocation in such path. To achieve it, this path reuses the
ucmd_buffer to copy user data. So the new data structures are added in
the ucmd_buffer union to avoid overflow."

[1] https://lore.kernel.org/linux-iommu/20230724111335.107427-8-yi.l.liu@intel.com/

> > 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.

Ok. so if any mistake on the data structure, the allocation fails in the first place.

Regards,
Yi Liu