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

[Dave Hansen <dave.hansen@intel.com>]

On 7/8/25 23:28, Lu Baolu wrote:
> 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.

The approach here is certainly conservative and simple. It's also not
going to cause big problems on systems without fancy IOMMUs.

But I am a _bit_ worried that it's _too_ conservative. The changelog
talks about page table page freeing, but the actual code:

> @@ -1540,6 +1541,7 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end)
>  		kernel_tlb_flush_range(info);
>  
>  	put_flush_tlb_info();
> +	iommu_sva_invalidate_kva_range(start, end);
>  }

is in a very generic TLB flushing spot that's used for a lot more than
just freeing page tables.

If the problem is truly limited to freeing page tables, it needs to be
commented appropriately.