LoongArch: Enable ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS

Provide support for CONFIG_MSEAL_SYSTEM_MAPPINGS on LoongArch, covering
the vdso.

Link: https://lore.kernel.org/all/25bad37f-273e-4626-999c-e1890be96182@lucifer.local/
Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Jeff Xu <jeffxu@chromium.org>
Tested-by: Yuli Wang <wangyuli@uniontech.com>
Signed-off-by: Yuli Wang <wangyuli@uniontech.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: Avenger-285714

Documentation/features/core/mseal_sys_mappings/arch-support.txt

@@ -12,7 +12,7 @@
     |       arm64: |  ok  |
     |        csky: |  N/A |
     |     hexagon: |  N/A |
-    |   loongarch: | TODO |
+    |   loongarch: |  ok  |
     |        m68k: |  N/A |
     |  microblaze: |  N/A |
     |        mips: | TODO |

Documentation/userspace-api/mseal.rst

@@ -144,7 +144,7 @@ Use cases
   architecture.
 
   The following architectures currently support this feature: x86-64, arm64,
-  and s390.
+  loongarch and s390.
 
   WARNING: This feature breaks programs which rely on relocating
   or unmapping system mappings. Known broken software at the time

arch/loongarch/Kconfig

@@ -69,6 +69,7 @@ config LOONGARCH
 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
 	select ARCH_SUPPORTS_LTO_CLANG
 	select ARCH_SUPPORTS_LTO_CLANG_THIN
+	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_SUPPORTS_RT
 	select ARCH_USE_BUILTIN_BSWAP

arch/loongarch/kernel/vdso.c

@@ -105,7 +105,9 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
 	vdso_addr = data_addr + VVAR_SIZE;
 	vma = _install_special_mapping(mm, vdso_addr, info->size,
-				       VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
+				       VM_READ | VM_EXEC |
+				       VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC |
+				       VM_SEALED_SYSMAP,
 				       &info->code_mapping);
 	if (IS_ERR(vma)) {
 		ret = PTR_ERR(vma);