From 81699345ccda59dfe27598799e5a2b038aa368f3 Mon Sep 17 00:00:00 2001
From: Dominique MARTINET <dominique.martinet@cea.fr>
Date: Fri, 25 May 2018 03:10:10 +0200
Subject: [PATCH] mprotect: do not set page table writable for cow pages

Change-Id: If8b0bb56e7dae59aa9dc3d745a4cc4e43bf4bf9a
---
 kernel/process.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/kernel/process.c b/kernel/process.c
index 3dda3ea7..377e0e08 100644
--- a/kernel/process.c
+++ b/kernel/process.c
@@ -1438,6 +1438,20 @@ int change_prot_process_memory_range(struct process_vm *vm,
 	clrattr = oldattr & ~newattr;
 	setattr = newattr & ~oldattr;
 
+	/*
+	 * If this is a file mapping don't set any new prot write.
+	 * We need to keep the page table read-only to trigger a page
+	 * fault for copy-on-write later on
+	 */
+	if (range->memobj && (range->flag & VR_PRIVATE)) {
+		setattr &= ~PTATTR_WRITABLE;
+		if (clrattr == setattr == 0) {
+			range->flag = newflag;
+			error = 0;
+			goto out;
+		}
+	}
+
 	ihk_mc_spinlock_lock_noirq(&vm->page_table_lock);
 	error = ihk_mc_pt_change_attr_range(vm->address_space->page_table,
 			(void *)range->start, (void *)range->end,