linux-kernel - Re: [PATCH 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

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Message-ID: <20250714133920.55fde0f5@pumpkin>
Date: Mon, 14 Jul 2025 13:39:20 +0100
From: David Laight <david.laight.linux@...il.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: jacob.pan@...ux.microsoft.com, Jason Gunthorpe <jgg@...dia.com>, Lu
 Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, Will
 Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>, Kevin Tian
 <kevin.tian@...el.com>, Jann Horn <jannh@...gle.com>, Vasant Hegde
 <vasant.hegde@....com>, Alistair Popple <apopple@...dia.com>, Peter
 Zijlstra <peterz@...radead.org>, Uladzislau Rezki <urezki@...il.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>, Andy Lutomirski
 <luto@...nel.org>, iommu@...ts.linux.dev, security@...nel.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

On Wed, 9 Jul 2025 11:22:34 -0700
Dave Hansen <dave.hansen@...el.com> wrote:

> On 7/9/25 11:15, Jacob Pan wrote:
> >>> Is there a use case where a SVA user can access kernel memory in the
> >>> first place?    
> >> No. It should be fully blocked.
> >>  
> > Then I don't understand what is the "vulnerability condition" being
> > addressed here. We are talking about KVA range here.  
> 
> SVA users can't access kernel memory, but they can compel walks of
> kernel page tables, which the IOMMU caches. The trouble starts if the
> kernel happens to free that page table page and the IOMMU is using the
> cache after the page is freed.
> 
> That was covered in the changelog, but I guess it could be made a bit
> more succinct.
> 

Is it worth just never freeing the page tables used for vmalloc() memory?
After all they are likely to be reallocated again.

That (should) only require IOMMU invalidate for pages that are actually
used for io.

	David