1 files changed, 104 insertions, 0 deletions
diff --git a/kernel/scs.c b/kernel/scs.c
new file mode 100644
index 000000000..4ff4a7ba0
--- /dev/null
+++ b/kernel/scs.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Shadow Call Stack support.
+ *
+ * Copyright (C) 2019 Google LLC
+ */
+
+#include <linux/kasan.h>
+#include <linux/mm.h>
+#include <linux/scs.h>
+#include <linux/slab.h>
+#include <linux/vmstat.h>
+
+static struct kmem_cache *scs_cache;
+
+static void __scs_account(void *s, int account)
+{
+	struct page *scs_page = virt_to_page(s);
+
+	mod_node_page_state(page_pgdat(scs_page), NR_KERNEL_SCS_KB,
+			    account * (SCS_SIZE / SZ_1K));
+}
+
+static void *scs_alloc(int node)
+{
+	void *s = kmem_cache_alloc_node(scs_cache, GFP_SCS, node);
+
+	if (!s)
+		return NULL;
+
+	*__scs_magic(s) = SCS_END_MAGIC;
+
+	/*
+	 * Poison the allocation to catch unintentional accesses to
+	 * the shadow stack when KASAN is enabled.
+	 */
+	kasan_poison_object_data(scs_cache, s);
+	__scs_account(s, 1);
+	return s;
+}
+
+static void scs_free(void *s)
+{
+	__scs_account(s, -1);
+	kasan_unpoison_object_data(scs_cache, s);
+	kmem_cache_free(scs_cache, s);
+}
+
+void __init scs_init(void)
+{
+	scs_cache = kmem_cache_create("scs_cache", SCS_SIZE, 0, 0, NULL);
+}
+
+int scs_prepare(struct task_struct *tsk, int node)
+{
+	void *s = scs_alloc(node);
+
+	if (!s)
+		return -ENOMEM;
+
+	task_scs(tsk) = task_scs_sp(tsk) = s;
+	return 0;
+}
+
+static void scs_check_usage(struct task_struct *tsk)
+{
+	static unsigned long highest;
+
+	unsigned long *p, prev, curr = highest, used = 0;
+
+	if (!IS_ENABLED(CONFIG_DEBUG_STACK_USAGE))
+		return;
+
+	for (p = task_scs(tsk); p < __scs_magic(tsk); ++p) {
+		if (!READ_ONCE_NOCHECK(*p))
+			break;
+		used += sizeof(*p);
+	}
+
+	while (used > curr) {
+		prev = cmpxchg_relaxed(&highest, curr, used);
+
+		if (prev == curr) {
+			pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",
+				tsk->comm, task_pid_nr(tsk), used);
+			break;
+		}
+
+		curr = prev;
+	}
+}
+
+void scs_release(struct task_struct *tsk)
+{
+	void *s = task_scs(tsk);
+
+	if (!s)
+		return;
+
+	WARN(task_scs_end_corrupted(tsk),
+	     "corrupted shadow stack detected when freeing task\n");
+	scs_check_usage(tsk);
+	scs_free(s);
+}