riscv: enable mseal sysmap for RV64

Provide support for CONFIG_MSEAL_SYSTEM_MAPPINGS for RV64, covering the
vdso, vvar.

Passed sysmap_is_sealed and mseal_test self tests.
Passed booting a buildroot rootfs image and a cli debian rootfs image.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Cc: Jeff Xu <jeffxu@chromium.org>
Link: https://lore.kernel.org/r/20250426135954.5614-1-jszhang@kernel.org
Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

Author: xhackerustc

arch/riscv/Kconfig

@@ -70,6 +70,7 @@ config RISCV
 	# LLD >= 14: https://github.com/llvm/llvm-project/issues/50505
 	select ARCH_SUPPORTS_LTO_CLANG if LLD_VERSION >= 140000
 	select ARCH_SUPPORTS_LTO_CLANG_THIN if LLD_VERSION >= 140000
+	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS if 64BIT && MMU
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK if MMU
 	select ARCH_SUPPORTS_PER_VMA_LOCK if MMU
 	select ARCH_SUPPORTS_RT

arch/riscv/kernel/vdso.c

@@ -136,7 +136,7 @@ static int __setup_additional_pages(struct mm_struct *mm,
 
 	ret =
 	   _install_special_mapping(mm, vdso_base, vdso_text_len,
-		(VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC),
+		(VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC | VM_SEALED_SYSMAP),
 		vdso_info->cm);
 
 	if (IS_ERR(ret))