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Wed, 05 Aug 2026 20:44:01 -0700 (PDT) Received: from Mac.lan ([125.128.148.126]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39085f2c714sm569978a91.10.2026.08.05.20.43.58 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 05 Aug 2026 20:44:01 -0700 (PDT) From: Baul Lee To: christian.koenig@amd.com, ray.huang@amd.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch Cc: matthew.auld@intel.com, matthew.brost@intel.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, federico.kirschbaum@xbow.com, stable@vger.kernel.org, Baul Lee Subject: [PATCH] drm/ttm: clamp the prefault window to the buffer object Date: Thu, 6 Aug 2026 12:43:56 +0900 Message-ID: <20260806034356.43681-1-baul.lee@xbow.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ttm_bo_vm_fault_reserved() derives two page indices from the caller's mmap(2) arguments and bounds only one of them: page_offset = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node); page_last = vma_pages(vma) + vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node); if (unlikely(page_offset >= PFN_UP(bo->base.size))) return VM_FAULT_SIGBUS; bo->base.size appears once in the function, bounding page_offset on entry. page_last comes straight from vma_pages(vma) and is the loop terminator: if (unlikely(++page_offset >= page_last)) break; so the object size never bounds it. For an object of N pages, a fault on the last in-object page passes the entry test with page_offset N - 1, and the prefault loop then walks N..N+14, reading ttm->pages[page_offset] or ttm_bo_io_mem_pfn(bo, page_offset) and installing each frame with vmf_insert_pfn_prot(). page_last exceeds the object whenever the VMA is longer than it. drm_gem_mmap_obj() rejects that on the DRM node, but the fbdev path reaches the object function through drm_gem_prime_mmap(), which does not. It is also exceeded by a mapping no longer than the object taken at a nonzero file offset, so the handler needs its own bound. With a 128-page object mapped 192 pages long, one read fault at index N - 1 leaves the fifteen frames after the object readable through the mapping; on a fresh mapping, reading index N without first faulting N - 1 is SIGBUS. For a system-memory placement the page array is over-read as well: BUG: KASAN: slab-out-of-bounds in ttm_bo_vm_fault_reserved+0x248/0x57c Read of size 8 at addr ffff0000078aac00 by task e1/219 __asan_load8+0x84/0xb0 ttm_bo_vm_fault_reserved+0x248/0x57c ttm_bo_vm_fault+0xe4/0x140 __do_fault+0x6c/0x2f0 Clamp page_last to the object. Discovered by XBOW, triaged by Baul Lee Fixes: ba4e7d973dd0 ("drm: Add the TTM GPU memory manager subsystem.") Cc: stable@vger.kernel.org Signed-off-by: Baul Lee --- drivers/gpu/drm/ttm/ttm_bo_vm.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c index a80510489c45..14ebf6ee3c47 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c @@ -212,6 +212,7 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf, vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node); page_last = vma_pages(vma) + vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node); + page_last = min_t(unsigned long, page_last, PFN_UP(bo->base.size)); if (unlikely(page_offset >= PFN_UP(bo->base.size))) return VM_FAULT_SIGBUS; -- 2.50.1 (Apple Git-155)