From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A93911A6807 for ; Fri, 3 Jul 2026 02:26:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783045586; cv=none; b=bJfircMu+TCHkbGYWUcBlgMzreGWaIVJ8bzhZbI5m7MjSTnkCUqXeAOB9NYyZXmLxectsSTpNBtY+2G/D1O3idqUc2ToAVUM+yXgdcfcdEhG38kyVE2JXBfjM1MJYviwOkYMGjy2puu8tc94dAi5IQihInFXIXNvIsvGgstPO3c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783045586; c=relaxed/simple; bh=T3XsEkIdyxoaeuMSiyD5B3ZHZUj9TDXqUjBQMbTBX/A=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=jD0DD8qtkKExlyXIwtInaVqbj6vQIw3ZriqIojcgtYOup+SquvSOwAMm6KhwG8vylj8GwO86GuShgNXzmAFg2z+NJBxg52wzChANMq7Q41YuEv1FVPkfWS4oqM9nvvZj9L1Gf/BzKTOCm4WnIgAwMATgdZx9GgKvBvIxWMPWx9o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=HAOh61zc; arc=none smtp.client-ip=91.218.175.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="HAOh61zc" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783045581; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=ZI0lTmkO/UHIT4+QlSIiK8ejRok32RfZUe5uhwcA5/U=; b=HAOh61zc+mozxiYtcPNEO5Yx8iORG5T8Mkpg/vMHNt2052hHUqbiQmAarZ6Dw+Wa155V9M 3s5333q3wzpR9SONk7wmKAVZRq1Oa6jrucylyEZauSAr7GDU5Puc5fP1m+9Lie//AcBW+2 G42rxvyD2sX024RzcWXP/b0U8+rU9uQ= From: Leon Hwang To: linux-mm@kvack.org Cc: Jonathan Corbet , Shuah Khan , Andrew Morton , "Liam R . Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pedro Falcato , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Leon Hwang , Nathan Chancellor , Peter Zijlstra , Miguel Ojeda , Nicolas Schier , Thomas Gleixner , =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= , Alice Ryhl , Douglas Anderson , Gary Guo , Anand Moon , Randy Dunlap , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: [PATCH] mm/mseal: fix mseal documentation for 32-bit kernels Date: Fri, 3 Jul 2026 10:25:07 +0800 Message-ID: <20260703022507.187457-1-leon.hwang@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT mseal.o is built only for 64-bit kernels, so 32-bit kernels fall back to sys_ni_syscall() and return -ENOSYS rather than -EPERM. Document the -EINTR return from mmap_write_lock_killable(), fix the CONFIG_MSEAL_SYSTEM_MAPPINGS typo, and describe system mappings in terms of VM_SEALED_SYSMAP. Signed-off-by: Leon Hwang --- Documentation/userspace-api/mseal.rst | 18 ++++++++++-------- init/Kconfig | 2 +- mm/mseal.c | 4 ++-- 3 files changed, 13 insertions(+), 11 deletions(-) diff --git a/Documentation/userspace-api/mseal.rst b/Documentation/userspace-api/mseal.rst index ea9b11a0bd89..1f1cf206670c 100644 --- a/Documentation/userspace-api/mseal.rst +++ b/Documentation/userspace-api/mseal.rst @@ -50,8 +50,10 @@ mseal syscall signature * The start address (``addr``) is not allocated. * The end address (``addr`` + ``len``) is not allocated. * A gap (unallocated memory) between start and end address. - - **-EPERM**: - * sealing is supported only on 64-bit CPUs, 32-bit is not supported. + - **-EINTR**: + * Interrupted while waiting for the mmap write lock. + - **-ENOSYS**: + * The kernel does not implement ``mseal()``. **Note about error return**: - For above error cases, users can expect the given memory range is @@ -62,7 +64,8 @@ mseal syscall signature memory range could happen. However, those cases should be rare. **Architecture support**: - mseal only works on 64-bit CPUs, not 32-bit CPUs. + mseal is built only for 64-bit kernels. 32-bit kernels return + ``-ENOSYS``. **Idempotent**: users can call mseal multiple times. mseal on an already sealed memory @@ -131,20 +134,19 @@ Use cases - Chrome browser: protect some security sensitive data structures. - System mappings: - The system mappings are created by the kernel and includes vdso, vvar, + The system mappings are created by the kernel and include vdso, vvar, vvar_vclock, vectors (arm compat-mode), sigpage (arm compat-mode), uprobes. Those system mappings are readonly only or execute only, memory sealing can - protect them from ever changing to writable or unmmap/remapped as different + protect them from ever changing to writable or unmapped/remapped as different attributes. This is useful to mitigate memory corruption issues where a corrupted pointer is passed to a memory management system. If supported by an architecture (CONFIG_ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS), - the CONFIG_MSEAL_SYSTEM_MAPPINGS seals all system mappings of this - architecture. + CONFIG_MSEAL_SYSTEM_MAPPINGS seals mappings marked with VM_SEALED_SYSMAP. The following architectures currently support this feature: x86-64, arm64, - loongarch and s390. + loongarch, riscv, and s390. WARNING: This feature breaks programs which rely on relocating or unmapping system mappings. Known broken software at the time diff --git a/init/Kconfig b/init/Kconfig index 5230d4879b1c..12bb39f637b1 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -2112,7 +2112,7 @@ config ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS from a kernel perspective. After the architecture enables this, a distribution can set - CONFIG_MSEAL_SYSTEM_MAPPING to manage access to the feature. + CONFIG_MSEAL_SYSTEM_MAPPINGS to manage access to the feature. For complete descriptions of memory sealing, please see Documentation/userspace-api/mseal.rst diff --git a/mm/mseal.c b/mm/mseal.c index 9781647483d1..0464c7b94ab9 100644 --- a/mm/mseal.c +++ b/mm/mseal.c @@ -132,8 +132,8 @@ static int mseal_apply(struct mm_struct *mm, * addr is not a valid address (not allocated). * end (start + len) is not a valid address. * a gap (unallocated memory) between start and end. - * -EPERM: - * - In 32 bit architecture, sealing is not supported. + * -EINTR: + * interrupted while waiting for the mmap write lock. * Note: * user can call mseal(2) multiple times, adding a seal on an * already sealed memory is a no-action (no error). -- 2.54.0