x86/vdso: Restrict splitting VVAR VMA

Forbid splitting VVAR VMA resulting in a stricter ABI and reducing the amount of corner-cases to consider while working further on VDSO time namespace support. As the offset from timens to VVAR page is computed compile-time, the pages in VVAR should stay together and not being partically mremap()'ed. Co-developed-by: Andrei Vagin <[email protected]> Signed-off-by: Andrei Vagin <[email protected]> Signed-off-by: Dmitry Safonov <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Link: https://lore.kernel.org/r/[email protected]
mj22226 · Jan 14, 2020 · 6f74acf · 6f74acf
1 parent 0efc8bb
commit 6f74acf
Showing 1 changed file with 13 additions and 0 deletions.
diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
@@ -84,6 +84,18 @@ static int vdso_mremap(const struct vm_special_mapping *sm,
 	return 0;
 }
 
+static int vvar_mremap(const struct vm_special_mapping *sm,
+		struct vm_area_struct *new_vma)
+{
+	const struct vdso_image *image = new_vma->vm_mm->context.vdso_image;
+	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
+
+	if (new_size != -image->sym_vvar_start)
+		return -EINVAL;
+
+	return 0;
+}
+
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
 		      struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -136,6 +148,7 @@ static const struct vm_special_mapping vdso_mapping = {
 static const struct vm_special_mapping vvar_mapping = {
 	.name = "[vvar]",
 	.fault = vvar_fault,
+	.mremap = vvar_mremap,
 };
 
 /*