From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 646023E5A35 for ; Fri, 3 Jul 2026 14:50:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783090252; cv=none; b=t8arBVpZ6pa1A8f7ycyo6LRznAKSy92FvuG6Kgxhn0jPUxnB+fVM8/t1TmBTihHb3gJ/2OoHOfZnZGWn32nVxCP3o2Ip0VMJ3rvtENb9RcJD/ES/FQgkAmiTIrQCfc8/3f3vLLcIXTUeH8CdnpWAGW0Tc7Qvn/hqxOn7M12GoNc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783090252; c=relaxed/simple; bh=D5ud8qWqRJ9MykIWJlRVr4bTYlYROne+B+OgA5icF38=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=F41/D/2XtP9Faqzqod0AqCAPy+yD+Y6IrptXKwTuhqN5+rCUmGuBYEvQTcDaxwEtnY6HwRJe4VZ8YGhG3HKBzyycfbJ9xRP6KIMCMIT/MLuOnWDda9J1wE+YcFWNlRn0v17X54H+9eerL6f91ggr0hQjREC4rzLjpIGUxNfiNuY= 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=UDBNB8/0; arc=none smtp.client-ip=91.218.175.188 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="UDBNB8/0" Message-ID: <8f75dc18-dd4c-4989-a76c-eec6cc513ccf@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783090246; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=CXlZY4gPG+zU33k3H0xm4g/0VaNA0tr7HNt5303WUBg=; b=UDBNB8/0B1x3/BrOa/t8tH6XYsteLhqIKb6sFPxo+8voiJoXwSGbGVTm7m2V2fKjxbZfG5 wYXqGIpNv/UsD7//6L9xKs/IvOligQC3lhghGNicG75MZUNKdc91kSBysgQAuIKoLqiQ3k zeQenTliY3QJ+tbtFUjK7MHFfZ7WXFo= Date: Fri, 3 Jul 2026 22:50:29 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] mm/mseal: fix mseal documentation for 32-bit kernels To: Pedro Falcato Cc: linux-mm@kvack.org, Jonathan Corbet , Shuah Khan , Andrew Morton , "Liam R . Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Nathan Chancellor , Peter Zijlstra , Miguel Ojeda , Nicolas Schier , Thomas Gleixner , =?UTF-8?Q?Thomas_Wei=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 References: <20260703022507.187457-1-leon.hwang@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Leon Hwang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/7/3 17:44, Pedro Falcato wrote: > On Fri, Jul 03, 2026 at 10:25:07AM +0800, Leon Hwang wrote: >> 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 > > Honestly, this whole thing needs to be deleted. We need a proper manpage. $ man mseal No manual entry for mseal When searching "mseal manual" using Google, this doc is the first entry. So, this change is worthy. > >> @@ -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``. > > This LGTM. > >> >> **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. > > Also LGTM. > >> >> 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. > > VM_SEALED_SYSMAP isn't meaningful to userspace. Got it. Will drop this change. > >> >> The following architectures currently support this feature: x86-64, arm64, >> - loongarch and s390. >> + loongarch, riscv, and s390. > > This is also useless, every 64-bit architecture will support this. Do you mean dropping this sentence, or this change? > >> >> 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). > > And this whole header needs to be deleted as well. No one's looking at > kernel code for documentation (and if they are, we did a horrendous job > at actually documenting the thing). > Just to confirm, do you mean removing the entire function comment above do_mseal()? Thanks, Leon