mseal sysmap: enable s390

Provide support for CONFIG_MSEAL_SYSTEM_MAPPINGS on s390, covering the
vdso.

[hca@linux.ibm.com: update supported architectures]
  Link: https://lkml.kernel.org/r/20250317131917.1332402-1-hca@linux.ibm.com
Link: https://lkml.kernel.org/r/20250311123326.2686682-3-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: hcahca

Documentation/userspace-api/mseal.rst

@@ -143,7 +143,8 @@ Use cases
   the CONFIG_MSEAL_SYSTEM_MAPPINGS seals all system mappings of this
   architecture.
 
-  The following architectures currently support this feature: x86-64 and arm64.
+  The following architectures currently support this feature: x86-64, arm64,
+  and s390.
 
   WARNING: This feature breaks programs which rely on relocating
   or unmapping system mappings. Known broken software at the time

arch/s390/Kconfig

@@ -137,6 +137,7 @@ config S390
 	select ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	select ARCH_SUPPORTS_HUGETLBFS
 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128 && CC_IS_CLANG
+	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select ARCH_USE_BUILTIN_BSWAP

arch/s390/kernel/vdso.c

@@ -80,7 +80,7 @@ static int map_vdso(unsigned long addr, unsigned long vdso_mapping_len)
 	vdso_text_start = vvar_start + VDSO_NR_PAGES * PAGE_SIZE;
 	/* VM_MAYWRITE for COW so gdb can set breakpoints */
 	vma = _install_special_mapping(mm, vdso_text_start, vdso_text_len,
-				       VM_READ|VM_EXEC|
+				       VM_READ|VM_EXEC|VM_SEALED_SYSMAP|
 				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 				       vdso_mapping);
 	if (IS_ERR(vma)) {