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[95.203.19.28]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-55943b77c64sm1956468e87.219.2025.07.14.06.19.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Jul 2025 06:19:20 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 14 Jul 2025 15:19:17 +0200 To: David Laight Cc: Dave Hansen , jacob.pan@linux.microsoft.com, Jason Gunthorpe , Lu Baolu , Joerg Roedel , Will Deacon , Robin Murphy , Kevin Tian , Jann Horn , Vasant Hegde , Alistair Popple , Peter Zijlstra , Uladzislau Rezki , Jean-Philippe Brucker , Andy Lutomirski , iommu@lists.linux.dev, security@kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush Message-ID: References: <20250704133056.4023816-1-baolu.lu@linux.intel.com> <20250709085158.0f050630@DESKTOP-0403QTC.> <20250709162724.GE1599700@nvidia.com> <20250709111527.5ba9bc31@DESKTOP-0403QTC.> <42c500b8-6ffb-4793-85c0-d3fbae0116f1@intel.com> <20250714133920.55fde0f5@pumpkin> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250714133920.55fde0f5@pumpkin> On Mon, Jul 14, 2025 at 01:39:20PM +0100, David Laight wrote: > On Wed, 9 Jul 2025 11:22:34 -0700 > Dave Hansen 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. > > Do we free? Maybe on some arches? According to my tests(AMD x86-64) i did once upon a time, the PTE entries were not freed after vfree(). It could be expensive if we did it, due to a global "page_table_lock" lock. I see one place though, it is in the vmap_try_huge_pud() if (pud_present(*pud) && !pud_free_pmd_page(pud, addr)) return 0; it is when replace a pud by a huge-page. -- Uladzislau Rezki