riscv: set the permission of vdso_data to read-only

The original vdso_data page is empty, so the permission of the vdso_data
page can be the same with the vdso text page. After introducing the vDSO
common flow, the vdso_data is not empty and the permission should be
changed to read-only.
Signed-off-by: NVincent Chen <vincent.chen@sifive.com>
Signed-off-by: NPalmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/kernel/vdso.c

@@ -79,13 +79,22 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
 	 */
 	mm->context.vdso = (void *)vdso_base;
 
-	ret = install_special_mapping(mm, vdso_base, vdso_len,
+	ret =
+	   install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
 		(VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC),
 		vdso_pagelist);
 
-	if (unlikely(ret))
+	if (unlikely(ret)) {
 		mm->context.vdso = NULL;
+		goto end;
+	}
 
+	vdso_base += (vdso_pages << PAGE_SHIFT);
+	ret = install_special_mapping(mm, vdso_base, PAGE_SIZE,
+		(VM_READ | VM_MAYREAD), &vdso_pagelist[vdso_pages]);
+
+	if (unlikely(ret))
+		mm->context.vdso = NULL;
 end:
 	up_write(&mm->mmap_sem);
 	return ret;
@@ -95,5 +104,8 @@ const char *arch_vma_name(struct vm_area_struct *vma)
 {
 	if (vma->vm_mm && (vma->vm_start == (long)vma->vm_mm->context.vdso))
 		return "[vdso]";
+	if (vma->vm_mm && (vma->vm_start ==
+			   (long)vma->vm_mm->context.vdso + PAGE_SIZE))
+		return "[vdso_data]";
 	return NULL;
 }