scs: Add support for Clang's Shadow Call Stack (SCS)

[linux-block.git] / kernel / scs.c

diff --git a/kernel/scs.c b/kernel/scs.c
new file mode 100644 (file)
index 0000000..38f8f31
--- /dev/null
+++ b/kernel/scs.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Shadow Call Stack support.
+ *
+ * Copyright (C) 2019 Google LLC
+ */
+
+#include <linux/kasan.h>
+#include <linux/scs.h>
+#include <linux/slab.h>
+#include <asm/scs.h>
+
+static struct kmem_cache *scs_cache;
+
+static void *scs_alloc(int node)
+{
+       void *s;
+
+       s = kmem_cache_alloc_node(scs_cache, GFP_SCS, node);
+       if (s) {
+               *__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);
+       }
+
+       return s;
+}
+
+static void scs_free(void *s)
+{
+       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) = s;
+       task_scs_offset(tsk) = 0;
+
+       return 0;
+}
+
+void scs_release(struct task_struct *tsk)
+{
+       void *s = task_scs(tsk);
+
+       if (!s)
+               return;
+
+       WARN(scs_corrupted(tsk), "corrupted shadow stack detected when freeing task\n");
+       scs_free(s);
+}