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Fri, 3 Jul 2026 09:44:21 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id vJYxF3WER2oBAgAAD6G6ig (envelope-from ); Fri, 03 Jul 2026 09:44:21 +0000 Date: Fri, 3 Jul 2026 10:44:19 +0100 From: Pedro Falcato To: Leon Hwang 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 , Thomas =?utf-8?Q?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 Subject: Re: [PATCH] mm/mseal: fix mseal documentation for 32-bit kernels Message-ID: References: <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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260703022507.187457-1-leon.hwang@linux.dev> X-Rspamd-Action: no action X-Rspamd-Queue-Id: 217FA747FE X-Spam-Flag: NO X-Spam-Score: -2.51 X-Spam-Level: X-Spamd-Result: default: False [-2.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[27]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; FREEMAIL_CC(0.00)[kvack.org,lwn.net,linuxfoundation.org,linux-foundation.org,infradead.org,kernel.org,google.com,dabbelt.com,eecs.berkeley.edu,ghiti.fr,linutronix.de,chromium.org,garyguo.net,gmail.com,vger.kernel.org,lists.infradead.org]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TAGGED_RCPT(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; R_RATELIMIT(0.00)[to_ip_from(RLaou5zaf46joj1hsq6ffhoiia)]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim,linux.dev:email] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org 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. > @@ -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. > > 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. > > 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). -- Pedro