From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f74.google.com (mail-wm1-f74.google.com [209.85.128.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7CBCB3382C7 for ; Fri, 9 Jan 2026 17:18:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767979095; cv=none; b=ecFHb0ym9gXze3r4Xulqs2RAk1Vlo6I8MePzuI5kJsGzSMEzcFprCR0eAGrk5+hC24sH0J26dpaK2FUejeWxFkQA12LobR1N7go0XouyuG5Mfa+uVMKXA9EAzGN88i0y4n9zvn86I4wPeCXSvZry5jbe8rH5BfwfohQYzY3TMFg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767979095; c=relaxed/simple; bh=MN7KwFeO9oAIogqgApPGUHmEWgErAJGaONG3a9YM5K4=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=P5aWoI9ngphv5SWBzVKNp1KZmUycEdWus7q9BtJDFAVtKRHVFeHBELaUNopl3AxnxKbU39NWfeahqRv+TbaJel0PBs7AC2/ppLEzKr5GTIS30gNJCU+uzk35lZfPMGrqPTfOK58/HkhhTcBiaR2ZPAybi5m39o0tIpaJaSfp3PM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--smostafa.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=ZNaLkeDC; arc=none smtp.client-ip=209.85.128.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--smostafa.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ZNaLkeDC" Received: by mail-wm1-f74.google.com with SMTP id 5b1f17b1804b1-47918084ac1so47535485e9.2 for ; Fri, 09 Jan 2026 09:18:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1767979092; x=1768583892; darn=lists.linux.dev; h=content-transfer-encoding:cc:to:from:subject:message-id :mime-version:date:from:to:cc:subject:date:message-id:reply-to; bh=EFPXi9jlv9rMnyA0grBQkKfopvHJmF7zvIc7VHv8N58=; b=ZNaLkeDC1aI5bJJWnvGhfKZeWFtK4hSIynYkSFZGkMWlmMVKTl5Cv6SsQYVj0HtBbQ MIRbLWYWfgM7YuECOCRFwfwo72MrHF0exiyu7MSj6c/MVuN+PcASs2S7hjG4FPqowXRU x8K4AUA4AuCycI9ckTYxG0T8b9t8a7V9nXdjAq3wWlDpqA/9Af22PGvnKBwm5uwFA4QM jOZ+xCie0REuFnh9/u1e6GzXOMcx9oyfxwLe1+cYy8/8tP6OEE0wdTihSN00I2wJ1No3 n2XLUqHYc5Ut7Q2zSsfDZre8gQC1VA1KMjccncv3Ah7Ijjb3mxsMA2gqgUR5lTB3dDpL H6Eg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1767979092; x=1768583892; h=content-transfer-encoding:cc:to:from:subject:message-id :mime-version:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=EFPXi9jlv9rMnyA0grBQkKfopvHJmF7zvIc7VHv8N58=; b=weNwZ5IYAZeafSm0Uiq3Fjc6bIUTeuw1GBasDTid8t1QZ8N+x4whb5khH3HOtks3AY iqEdeT2dtQNoekws03fG1k+x7OLvfXcv127Xxcxpr6eA/9XaDt02ARLkGAxCqdvGItM6 zYFGJ+Kl1fb5+zFRj83qBQ9pJOBrZ0ShzTLJ1d08jtHY7kbLcqtv0kH25fLwdBTHCQxU XuCsuGTWj1LFi7hsNAaXEyhOyeXUEKqa/3f/QT/YV0VMa2STC2HKjxMc0sPl0iswtm8l brZfBOwVhpmcYV9SlOt/qpanNRoZMWpgP78sN3KQ87k4X97Sh363SkJ62TClCC5hw1A4 PcAQ== X-Forwarded-Encrypted: i=1; AJvYcCUFraBSmV1bmAhoVhmNEP5L9O5rOjKF7Mx12y5tkCejLyiO8tpuxZ4WsyLV9DJenofzeUCusg==@lists.linux.dev X-Gm-Message-State: AOJu0YznNHnkafwa3tNXT6zAYxJhDDOs+JpivUIn3C2LNDhS/ZZnLSxl +7zcgd/7ZypMCYZkvQHHuXKtM7jnTBva8FHpfAbyonFJv9i/YqNge/VJl+MO0pN3ijOXgE8p6CP NVq3cgvkE8W9ENg== X-Google-Smtp-Source: AGHT+IFocuqh4xf3N3PNsIA9bVyZchbl85zeIdFnVspAH2mPKuFwxxYp6oh+Bwc2UYAh9iIB3e8vzhQ1q9OD3A== X-Received: from wmba20.prod.google.com ([2002:a05:600c:6dd4:b0:47b:d5ad:dd7f]) (user=smostafa job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:1d14:b0:477:97c7:9be7 with SMTP id 5b1f17b1804b1-47d84b0a7bdmr116367135e9.1.1767979092009; Fri, 09 Jan 2026 09:18:12 -0800 (PST) Date: Fri, 9 Jan 2026 17:18:01 +0000 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.52.0.457.g6b5491de43-goog Message-ID: <20260109171805.901995-1-smostafa@google.com> Subject: [PATCH v6 0/4] iommu: Add page_ext for IOMMU_DEBUG_PAGEALLOC From: Mostafa Saleh To: linux-mm@kvack.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Cc: corbet@lwn.net, joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, xiaqinxin@huawei.com, baolu.lu@linux.intel.com, rdunlap@infradead.org, Mostafa Saleh Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Overview -------- This patch series introduces a new debugging feature, IOMMU_DEBUG_PAGEALLOC, designed to catch DMA use-after-free bugs and IOMMU mapping leaks from buggy drivers. The kernel has powerful sanitizers like KASAN and DEBUG_PAGEALLOC for catching CPU-side memory corruption. However, there is limited runtime sanitization for DMA mappings managed by the IOMMU. A buggy driver can free a page while it is still mapped for DMA, leading to memory corruption or use-after-free vulnerabilities when that page is reallocated and used for a different purpose. Inspired by DEBUG_PAGEALLOC, this sanitizer tracks IOMMU mappings on a per-page basis, as it=E2=80=99s not possible to unmap the pages, because it requires to lock and walk all domains on every kernel free, instead we rely on page_ext to add an IOMMU-specific mapping reference count for each page. And on each page allocated/freed from the kernel we simply check the count and WARN if it is not zero, and dumping page owner information if enabled. Concurrency ----------- By design this check is racy where one caller can map pages just after the check, which can lead to false negatives. In my opinion this is acceptable for sanitizers (for ex KCSAN have that property). Otherwise we have to implement locks in iommu_map/unmap for all domains which is not favourable even for a debug feature. The sanitizer only guarantees that the refcount itself doesn=E2=80=99t get corrupted using atomics. And there are no false positives. CPU vs IOMMU Page Size ---------------------- IOMMUs can use different page sizes and which can be non-homogeneous; not even all of them have the same page size. To solve this, the refcount is always incremented and decremented in units of the smallest page size supported by the IOMMU domain. This ensures the accounting remains consistent regardless of the size of the map or unmap operation, otherwise double counting can happen. Testing & Performance --------------------- This was tested on Morello with Arm64 + SMMUv3 Did some testing Lenovo IdeaCentre X Gen 10 Snapdragon Did some testing on Qemu including different SMMUv3/CPU page size (arm64). I also ran dma_map_benchmark on Morello: echo dma_map_benchmark > /sys/bus/pci/devices/0000\:06\:00.0/driver_overrid= e echo 0000:06:00.0 > /sys/bus/pci/devices/0000\:06\:00.0/driver/unbind echo 0000:06:00.0 > /sys/bus/pci/drivers/dma_map_benchmark/bind ./dma_map_benchmark -t $threads -g $nr_pages CONFIG refers to "CONFIG_IOMMU_DEBUG_PAGEALLOC" cmdline refers to "iommu.debug_pagealloc" Numbers are (map latency)/(unmap latency), lower is better. CONFIG=3Dn CONFIG=3Dy CONFIG=3Dy cmdline=3D0 cmdline=3D1 4K - 1 thread 0.1/0.6 0.1/0.6 0.1/0.7 4K - 4 threads 0.1/1.1 0.1/1.0 0.2/1.1 1M - 1 thread 0.8/21.2 0.7/21.2 5.4/42.3 1M - 4 threads 1.1/45.9 1.1/46.0 5.9/45.1 Changes in v6: v5: https://lore.kernel.org/linux-iommu/20260106162200.2223655-1-smostafa@g= oogle.com/ - Remove wrong logic for handling unmap with bigger size than requested and warn instead. - Collect R-bs and Acked-by Changes in v5: v4: https://lore.kernel.org/all/20251211125928.3258905-1-smostafa@google.co= m/ - Fix typo in comment - Collect Baolu R-bs Main changes in v4: v3: https://lore.kernel.org/all/20251124200811.2942432-1-smostafa@google.co= m/ - Update the kernel parameter format in docs based on Randy feedback - Update commit subjects - Add IOMMU only functions in iommu-priv.h based on Baolu feedback Main changes in v3: (Most of them addressing Will comments) v2: https://lore.kernel.org/linux-iommu/20251106163953.1971067-1-smostafa@g= oogle.com/ - Reword the Kconfig help - Use unmap_begin/end instead of unmap/remap - Use relaxed accessors when refcounting - Fix a bug with checking the returned address from iova_to_phys - Add more hardening checks (overflow) - Add more debug info on assertions (dump_page_owner()) - Handle cases where unmap returns larger size as the core code seems to tolerate that. - Drop Tested-by tags from Qinxin as the code logic changed Main changes in v2: v1: https://lore.kernel.org/linux-iommu/20251003173229.1533640-1-smostafa@g= oogle.com/ - Address J=C3=B6rg comments about #ifdefs and static keys - Reword the Kconfig help - Drop RFC - Collect t-b from Qinxin - Minor cleanups Mostafa Saleh (4): iommu: Add page_ext for IOMMU_DEBUG_PAGEALLOC iommu: Add calls for IOMMU_DEBUG_PAGEALLOC iommu: debug-pagealloc: Track IOMMU pages iommu: debug-pagealloc: Check mapped/unmapped kernel memory .../admin-guide/kernel-parameters.txt | 9 + drivers/iommu/Kconfig | 19 ++ drivers/iommu/Makefile | 1 + drivers/iommu/iommu-debug-pagealloc.c | 167 ++++++++++++++++++ drivers/iommu/iommu-priv.h | 58 ++++++ drivers/iommu/iommu.c | 11 +- include/linux/iommu-debug-pagealloc.h | 32 ++++ include/linux/mm.h | 5 + mm/page_ext.c | 4 + 9 files changed, 304 insertions(+), 2 deletions(-) create mode 100644 drivers/iommu/iommu-debug-pagealloc.c create mode 100644 include/linux/iommu-debug-pagealloc.h --=20 2.52.0.457.g6b5491de43-goog