add canary to kernel stack

1 files changed, 39 insertions, 0 deletions

diff --git a/common/canary.c b/common/canary.c
new file mode 100644
index 0000000..9fd89ff
--- /dev/null
+++ b/common/canary.c
@@ -0,0 +1,39 @@
+#include <apos/canary.h>
+#include <apos/mem.h>
+
+/**
+ * @file canary.c
+ * Kernel stack canary implementation.
+ */
+
+/** Typedef for canary value type. */
+typedef uint32_t canary_t;
+
+/** Canary magic value. */
+static const canary_t canary = 0xb00b1e5;
+
+/**
+ * Helper for calculating the canary location of \p t.
+ *
+ * @param t \ref tcb to calculate canary position of.
+ * @return Pointer to canary location, that is bottom of stack.
+ * \todo This assumes that all stacks grow downwards. Unlikely to ever be
+ * ported to a platform that doesn't abide by this, but keep it in mind anyway.
+ */
+static canary_t *get_canary(struct tcb *t)
+{
+	size_t s = order_size(KERNEL_STACK_PAGE_ORDER);
+	return (canary_t *)align_down((uintptr_t)t, s);
+}
+
+void set_canary(struct tcb *t)
+{
+	canary_t *c = get_canary(t);
+	*c = canary;
+}
+
+bool check_canary(struct tcb *t)
+{
+	canary_t *c = get_canary(t);
+	return *c != canary;
+}