[PATCH] mm/mseal: fix mseal documentation for 32-bit kernels
From: Leon Hwang <hidden>
Date: 2026-07-03 02:26:34
Also in:
linux-mm, linux-riscv, lkml
Subsystem:
documentation, memory management, memory mapping, the rest · Maintainers:
Jonathan Corbet, Andrew Morton, Liam R. Howlett, Lorenzo Stoakes, Linus Torvalds
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 <redacted> --- 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