6.18-stable review patch. If anyone has any objections, please let me know.
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From: Lu Baolu baolu.lu@linux.intel.com
commit 72f98ef9a4be30d2a60136dd6faee376f780d06c upstream.
Patch series "Fix stale IOTLB entries for kernel address space", v7.
This proposes a fix for a security vulnerability related to IOMMU Shared Virtual Addressing (SVA). In an SVA context, an IOMMU can cache kernel page table entries. When a kernel page table page is freed and reallocated for another purpose, the IOMMU might still hold stale, incorrect entries. This can be exploited to cause a use-after-free or write-after-free condition, potentially leading to privilege escalation or data corruption.
This solution introduces a deferred freeing mechanism for kernel page table pages, which provides a safe window to notify the IOMMU to invalidate its caches before the page is reused.
This patch (of 8):
In the IOMMU Shared Virtual Addressing (SVA) context, the IOMMU hardware shares and walks the CPU's page tables. The x86 architecture maps the kernel's virtual address space into the upper portion of every process's page table. Consequently, in an SVA context, the IOMMU hardware can walk and cache kernel page table entries.
The Linux kernel currently lacks a notification mechanism for kernel page table changes, specifically when page table pages are freed and reused. The IOMMU driver is only notified of changes to user virtual address mappings. This can cause the IOMMU's internal caches to retain stale entries for kernel VA.
Use-After-Free (UAF) and Write-After-Free (WAF) conditions arise when kernel page table pages are freed and later reallocated. The IOMMU could misinterpret the new data as valid page table entries. The IOMMU might then walk into attacker-controlled memory, leading to arbitrary physical memory DMA access or privilege escalation. This is also a Write-After-Free issue, as the IOMMU will potentially continue to write Accessed and Dirty bits to the freed memory while attempting to walk the stale page tables.
Currently, SVA contexts are unprivileged and cannot access kernel mappings. However, the IOMMU will still walk kernel-only page tables all the way down to the leaf entries, where it realizes the mapping is for the kernel and errors out. This means the IOMMU still caches these intermediate page table entries, making the described vulnerability a real concern.
Disable SVA on x86 architecture until the IOMMU can receive notification to flush the paging cache before freeing the CPU kernel page table pages.
Link: https://lkml.kernel.org/r/20251022082635.2462433-1-baolu.lu@linux.intel.com Link: https://lkml.kernel.org/r/20251022082635.2462433-2-baolu.lu@linux.intel.com Fixes: 26b25a2b98e4 ("iommu: Bind process address spaces to devices") Signed-off-by: Lu Baolu baolu.lu@linux.intel.com Suggested-by: Jason Gunthorpe jgg@nvidia.com Reviewed-by: Jason Gunthorpe jgg@nvidia.com Cc: Alistair Popple apopple@nvidia.com Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Betkov bp@alien8.de Cc: Dave Hansen dave.hansen@intel.com Cc: David Hildenbrand david@redhat.com Cc: Ingo Molnar mingo@redhat.com Cc: Jann Horn jannh@google.com Cc: Jean-Philippe Brucker jean-philippe@linaro.org Cc: Joerg Roedel joro@8bytes.org Cc: Kevin Tian kevin.tian@intel.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Michal Hocko mhocko@kernel.org Cc: Mike Rapoport rppt@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Robin Murohy robin.murphy@arm.com Cc: Thomas Gleinxer tglx@linutronix.de Cc: "Uladzislau Rezki (Sony)" urezki@gmail.com Cc: Vasant Hegde vasant.hegde@amd.com Cc: Vinicius Costa Gomes vinicius.gomes@intel.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Will Deacon will@kernel.org Cc: Yi Lai yi1.lai@intel.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/iommu/iommu-sva.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/drivers/iommu/iommu-sva.c +++ b/drivers/iommu/iommu-sva.c @@ -77,6 +77,9 @@ struct iommu_sva *iommu_sva_bind_device( if (!group) return ERR_PTR(-ENODEV);
+ if (IS_ENABLED(CONFIG_X86)) + return ERR_PTR(-EOPNOTSUPP); + mutex_lock(&iommu_sva_lock);
/* Allocate mm->pasid if necessary. */