linux-kernel - RE: [PATCH v2 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

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Message-ID: <BN9PR11MB52765F651EBE0988E35E15FF8C48A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Thu, 10 Jul 2025 03:02:07 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, "Will
 Deacon" <will@...nel.org>, Robin Murphy <robin.murphy@....com>, "Jason
 Gunthorpe" <jgg@...dia.com>, Jann Horn <jannh@...gle.com>, Vasant Hegde
	<vasant.hegde@....com>, "Hansen, Dave" <dave.hansen@...el.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>, "Lai, Yi1"
	<yi1.lai@...el.com>
CC: "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, "security@...nel.org"
	<security@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "stable@...r.kernel.org"
	<stable@...r.kernel.org>
Subject: RE: [PATCH v2 1/1] iommu/sva: Invalidate KVA range on kernel TLB
 flush

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Wednesday, July 9, 2025 2:28 PM
> 
> The vmalloc() and vfree() functions manage virtually contiguous, but not
> necessarily physically contiguous, kernel memory regions. When vfree()
> unmaps such a region, it tears down the associated kernel page table
> entries and frees the physical pages.
> 
> In the IOMMU Shared Virtual Addressing (SVA) context, the IOMMU
> hardware
> shares and walks the CPU's page tables. Architectures like x86 share
> static kernel address mappings across all user page tables, allowing the

I'd remove 'static'

> IOMMU to access the kernel portion of these tables.
> 
> Modern IOMMUs often cache page table entries to optimize walk
> performance,
> even for intermediate page table levels. If kernel page table mappings are
> changed (e.g., by vfree()), but the IOMMU's internal caches retain stale
> entries, Use-After-Free (UAF) vulnerability condition arises. If these
> freed page table pages are reallocated for a different purpose, potentially
> by an attacker, the IOMMU could misinterpret the new data as valid page
> table entries. This allows the IOMMU to walk into attacker-controlled
> memory, leading to arbitrary physical memory DMA access or privilege
> escalation.

this lacks of a background that currently the iommu driver is notified
only for changes of user VA mappings, so the IOMMU's internal caches
may retain stale entries for kernel VA.

> 
> To mitigate this, introduce a new iommu interface to flush IOMMU caches
> and fence pending page table walks when kernel page mappings are updated.
> This interface should be invoked from architecture-specific code that
> manages combined user and kernel page tables.

this also needs some words about the fact that new flushes are triggered
not just for freeing page tables.

> 
>  static DEFINE_MUTEX(iommu_sva_lock);
> +static DEFINE_STATIC_KEY_FALSE(iommu_sva_present);
> +static LIST_HEAD(iommu_sva_mms);
> +static DEFINE_SPINLOCK(iommu_mms_lock);

s/iommu_mms_lock/iommu_mm_lock/

Reviewed-by: Kevin Tian <kevin.tian@...el.com>