linux-kernel - Re: [PATCH v5 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master invalidation array

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

Message-ID: <20251124230845.GN153257@nvidia.com>
Date: Mon, 24 Nov 2025 19:08:45 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Will Deacon <will@...nel.org>, jean-philippe@...aro.org,
	robin.murphy@....com, joro@...tes.org, balbirs@...dia.com,
	miko.lenczewski@....com, peterz@...radead.org, kevin.tian@...el.com,
	praan@...gle.com, linux-arm-kernel@...ts.infradead.org,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master
 invalidation array

On Mon, Nov 24, 2025 at 02:43:58PM -0800, Nicolin Chen wrote:
> On Mon, Nov 24, 2025 at 09:42:55PM +0000, Will Deacon wrote:
> > On Sat, Nov 08, 2025 at 12:08:05AM -0800, Nicolin Chen wrote:
> > > +		/* Put the ids into order for sorted to_merge/to_unref arrays */
> > > +		sort_nonatomic(fwspec->ids, fwspec->num_ids,
> > > +			       sizeof(fwspec->ids[0]), arm_smmu_ids_cmp, NULL);
> > > +		/* ATS case adds num_ids of entries, on top of the base case */
> > > +		master->build_invs = arm_smmu_invs_alloc(2 + fwspec->num_ids);
> > 
> > Although I can't point at a specific issue here, I'm nervous about mutating
> > the 'fwspec->ids' array from within the driver, The array isn't allocated
> > or populated directly by the driver and so I don't think we really have any
> > business sorting it. Could we hack iommu_fwspec_add_ids() to keep the array
> > ordered instead?
> 
> Yea, I think it makes sense to do it in the core, once we have the
> data structure provided by the core as well.

I would be more worried about sorting it everywhere for every
driver. I feel confident SMMUv3 doesn't use it, but something really
old and embedded focused like tegra or omap, IDK.

So I wouldn't propose to change iommu_fwspec_add_ids().

If you want to be conservative then the thing to do is sort the
master->streams that arm_smmu_insert_master() copies the fwspec
into. It just has to be sorted prior to feeding it into the rbtree.

Then consistently use master->streams as the sorted list.

Jason