powerpc/vdso: Provide vdso_remap()

Provide vdso_remap() through _install_special_mapping() and
drop arch_remap().

This adds a test of the size and returns -EINVAL if the size
is not correct.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/373c66f768fa9cc8890f3b55462209a98c522326.1601197618.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/mm-arch-hooks.h

-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Architecture specific mm hooks
- *
- * Copyright (C) 2015, IBM Corporation
- * Author: Laurent Dufour <ldufour@linux.vnet.ibm.com>
- */
-
-#ifndef _ASM_POWERPC_MM_ARCH_HOOKS_H
-#define _ASM_POWERPC_MM_ARCH_HOOKS_H
-
-static inline void arch_remap(struct mm_struct *mm,
-			      unsigned long old_start, unsigned long old_end,
-			      unsigned long new_start, unsigned long new_end)
-{
-	/*
-	 * mremap() doesn't allow moving multiple vmas so we can limit the
-	 * check to old_start == vdso_base.
-	 */
-	if (old_start == mm->context.vdso_base)
-		mm->context.vdso_base = new_start;
-}
-#define arch_remap arch_remap
-
-#endif /* _ASM_POWERPC_MM_ARCH_HOOKS_H */

arch/powerpc/kernel/vdso.c

@@ -115,13 +115,37 @@ struct lib64_elfinfo
 	unsigned long	text;
 };
 
+static int vdso_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma,
+		       unsigned long text_size)
+{
+	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
+
+	if (new_size != text_size + PAGE_SIZE)
+		return -EINVAL;
+
+	current->mm->context.vdso_base = new_vma->vm_start;
+
+	return 0;
+}
+
+static int vdso32_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma)
+{
+	return vdso_mremap(sm, new_vma, &vdso32_end - &vdso32_start);
+}
+
+static int vdso64_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma)
+{
+	return vdso_mremap(sm, new_vma, &vdso64_end - &vdso64_start);
+}
 
 static struct vm_special_mapping vdso32_spec __ro_after_init = {
 	.name = "[vdso]",
+	.mremap = vdso32_mremap,
 };
 
 static struct vm_special_mapping vdso64_spec __ro_after_init = {
 	.name = "[vdso]",
+	.mremap = vdso64_mremap,
 };
 
 /*