From 6f74acfde20af1eb2178d0bd846bfd8f50b3be32 Mon Sep 17 00:00:00 2001
From: Dmitry Safonov <dima@arista.com>
Date: Tue, 12 Nov 2019 01:27:08 +0000
Subject: [PATCH 19/34] x86/vdso: Restrict splitting VVAR VMA
Git-commit: 6f74acfde20af1eb2178d0bd846bfd8f50b3be32
Patch-mainline: v5.6-rc1
References: bsc#1164648,jsc#SLE-11493

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 <avagin@openvz.org>
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20191112012724.250792-20-dima@arista.com
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>

---
 arch/x86/entry/vdso/vma.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index f5937742b290..76cbe54e0c39 100644
--- 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,
 };
 
 /*
-- 
2.16.4