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Wed, 05 Aug 2026 20:43:48 -0700 (PDT) Received: from Mac.lan ([125.128.148.126]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d0aa4c911esm23899715ad.66.2026.08.05.20.43.45 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 05 Aug 2026 20:43:48 -0700 (PDT) From: Baul Lee To: patrik.r.jakobsson@gmail.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, federico.kirschbaum@xbow.com, stable@vger.kernel.org, Baul Lee Subject: [PATCH] drm/gma500: bound the fbdev fault loop to the framebuffer Date: Thu, 6 Aug 2026 12:43:43 +0900 Message-ID: <20260806034343.43629-1-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 psb_fbdev_vm_fault() maps as many frames as the caller asked for: unsigned long pfn = info->fix.smem_start >> PAGE_SHIFT; unsigned long page_num = vma_pages(vma); for (i = 0; i < page_num; ++i) { err = vmf_insert_mixed(vma, address, pfn); ... address += PAGE_SIZE; ++pfn; } The trip count is the VMA length and the pfn walks up from the framebuffer base. info->fix.smem_len, the extent of the framebuffer, is not read anywhere in the handler, so a mapping longer than the framebuffer installs present PTEs for the physical frames above it. Nothing else on the path bounds the length. psb_fbdev_fb_mmap() only requires vm_pgoff to be zero, and fb_mmap() passes the length through. On x86_64 an unprivileged process in group video mapped 4800 pages of a 600-page framebuffer; every page was present and writable, and the 4200 past the object were the frames above it in physical memory. Nothing is logged: the kernel installs valid PTEs and every access through them comes from userspace. Reject a fault whose page offset is already past the framebuffer and clamp the loop to the frames the framebuffer owns. Discovered by XBOW, triaged by Baul Lee Fixes: 0867b42113ec ("staging: gma500: Intel GMA500 staging driver") Cc: stable@vger.kernel.org Signed-off-by: Baul Lee --- drivers/gpu/drm/gma500/fbdev.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/gpu/drm/gma500/fbdev.c b/drivers/gpu/drm/gma500/fbdev.c index d1e93588234f..393a939a0c37 100644 --- a/drivers/gpu/drm/gma500/fbdev.c +++ b/drivers/gpu/drm/gma500/fbdev.c @@ -26,9 +26,15 @@ static vm_fault_t psb_fbdev_vm_fault(struct vm_fault *vmf) unsigned long address = vmf->address - (vmf->pgoff << PAGE_SHIFT); unsigned long pfn = info->fix.smem_start >> PAGE_SHIFT; vm_fault_t err = VM_FAULT_SIGBUS; + unsigned long obj_pages = info->fix.smem_len >> PAGE_SHIFT; unsigned long page_num = vma_pages(vma); unsigned long i; + if (vmf->pgoff >= obj_pages) + return VM_FAULT_SIGBUS; + if (page_num > obj_pages) + page_num = obj_pages; + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); for (i = 0; i < page_num; ++i) { -- 2.50.1 (Apple Git-155)