linux-kernel - Re: [PATCH v3 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

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Message-ID: <20250806155223.GV184255@nvidia.com>
Date: Wed, 6 Aug 2025 12:52:23 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: 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>, Yi Lai <yi1.lai@...el.com>,
	iommu@...ts.linux.dev, security@...nel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3 1/1] iommu/sva: Invalidate KVA range on kernel TLB
 flush

On Wed, Aug 06, 2025 at 08:03:42AM -0700, Dave Hansen wrote:
> Hold on a sec, though. the problematic caller of this looks something
> like this (logically):
> 
> 	pmd_free_pte_page()
> 	{
> 	        pte = pmd_page_vaddr(*pmd);
> 	        pmd_clear(pmd);
> 		flush_tlb_kernel_range(...); // does schedule_work()
> 		pte_free_kernel(pte);
> 	}
> 
> It _immediately_ frees the PTE page. The schedule_work() work will
> probably happen sometime after the page is freed.
> 
> Isn't that still a use-after-free? It's for some arbitrary amount of
> time and better than before but it's still a use-after-free.

Yes it is.

You can't do this approach without also pushing the pages to freed on
a list and defering the free till the work. This is broadly what the
normal mm user flow is doing..

Jason