1 files changed, 34 insertions, 20 deletions

diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index aeed1c2aaf3c..47f98d87ea3c 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -14,11 +14,14 @@
 #include <as-layout.h>
 #include <os.h>
 #include <skas.h>
+#include <stub-data.h>
+
+/* Ensure the stub_data struct covers the allocated area */
+static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
 
 int init_new_context(struct task_struct *task, struct mm_struct *mm)
 {
- 	struct mm_context *from_mm = NULL;
-	struct mm_context *to_mm = &mm->context;
+	struct mm_id *new_id = &mm->context.id;
 	unsigned long stack = 0;
 	int ret = -ENOMEM;
 
@@ -26,34 +29,46 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm)
 	if (stack == 0)
 		goto out;
 
-	to_mm->id.stack = stack;
-	if (current->mm != NULL && current->mm != &init_mm)
-		from_mm = &current->mm->context;
+	new_id->stack = stack;
 
 	block_signals_trace();
-	if (from_mm)
-		to_mm->id.u.pid = copy_context_skas0(stack,
-						     from_mm->id.u.pid);
-	else to_mm->id.u.pid = start_userspace(stack);
+	new_id->u.pid = start_userspace(stack);
 	unblock_signals_trace();
 
-	if (to_mm->id.u.pid < 0) {
-		ret = to_mm->id.u.pid;
+	if (new_id->u.pid < 0) {
+		ret = new_id->u.pid;
 		goto out_free;
 	}
 
-	ret = init_new_ldt(to_mm, from_mm);
-	if (ret < 0) {
-		printk(KERN_ERR "init_new_context_skas - init_ldt"
-		       " failed, errno = %d\n", ret);
-		goto out_free;
-	}
+	/*
+	 * Ensure the new MM is clean and nothing unwanted is mapped.
+	 *
+	 * TODO: We should clear the memory up to STUB_START to ensure there is
+	 * nothing mapped there, i.e. we (currently) have:
+	 *
+	 * |- user memory -|- unused        -|- stub        -|- unused    -|
+	 *                 ^ TASK_SIZE      ^ STUB_START
+	 *
+	 * Meaning we have two unused areas where we may still have valid
+	 * mappings from our internal clone(). That isn't really a problem as
+	 * userspace is not going to access them, but it is definitely not
+	 * correct.
+	 *
+	 * However, we are "lucky" and if rseq is configured, then on 32 bit
+	 * it will fall into the first empty range while on 64 bit it is going
+	 * to use an anonymous mapping in the second range. As such, things
+	 * continue to work for now as long as we don't start unmapping these
+	 * areas.
+	 *
+	 * Change this to STUB_START once we have a clean userspace.
+	 */
+	unmap(new_id, 0, TASK_SIZE);
 
 	return 0;
 
  out_free:
-	if (to_mm->id.stack != 0)
-		free_pages(to_mm->id.stack, ilog2(STUB_DATA_PAGES));
+	if (new_id->stack != 0)
+		free_pages(new_id->stack, ilog2(STUB_DATA_PAGES));
  out:
 	return ret;
 }
@@ -76,5 +91,4 @@ void destroy_context(struct mm_struct *mm)
 	os_kill_ptraced_process(mmu->id.u.pid, 1);
 
 	free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES));
-	free_ldt(mmu);
 }