1 files changed, 307 insertions, 0 deletions
diff --git a/kernel/cfi.c b/kernel/cfi.c
new file mode 100644
index 000000000000..967b0755c00e
--- /dev/null
+++ b/kernel/cfi.c
@@ -0,0 +1,307 @@
+/*
+ * CFI (Control Flow Integrity) error and slowpath handling
+ *
+ * Copyright (C) 2017 Google, Inc.
+ */
+
+#include <linux/gfp.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/ratelimit.h>
+#include <linux/rcupdate.h>
+#include <linux/spinlock.h>
+#include <asm/bug.h>
+#include <asm/cacheflush.h>
+#include <asm/memory.h>
+#include <asm/set_memory.h>
+
+/* Compiler-defined handler names */
+#ifdef CONFIG_CFI_PERMISSIVE
+#define cfi_failure_handler	__ubsan_handle_cfi_check_fail
+#define cfi_slowpath_handler	__cfi_slowpath_diag
+#else /* enforcing */
+#define cfi_failure_handler	__ubsan_handle_cfi_check_fail_abort
+#define cfi_slowpath_handler	__cfi_slowpath
+#endif /* CONFIG_CFI_PERMISSIVE */
+
+static inline void handle_cfi_failure(void *ptr)
+{
+#ifdef CONFIG_CFI_PERMISSIVE
+	WARN_RATELIMIT(1, "CFI failure (target: [<%px>] %pF):\n", ptr, ptr);
+#else
+	pr_err("CFI failure (target: [<%px>] %pF):\n", ptr, ptr);
+	BUG();
+#endif
+}
+
+#ifdef CONFIG_MODULES
+#ifdef CONFIG_CFI_CLANG_SHADOW
+struct shadow_range {
+	/* Module address range */
+	unsigned long mod_min_addr;
+	unsigned long mod_max_addr;
+	/* Module page range */
+	unsigned long min_page;
+	unsigned long max_page;
+};
+
+#define SHADOW_ORDER	1
+#define SHADOW_PAGES	(1 << SHADOW_ORDER)
+#define SHADOW_SIZE \
+	((SHADOW_PAGES * PAGE_SIZE - sizeof(struct shadow_range)) / sizeof(u16))
+#define SHADOW_INVALID	0xFFFF
+
+struct cfi_shadow {
+	/* Page range covered by the shadow */
+	struct shadow_range r;
+	/* Page offsets to __cfi_check functions in modules */
+	u16 shadow[SHADOW_SIZE];
+};
+
+static DEFINE_SPINLOCK(shadow_update_lock);
+static struct cfi_shadow __rcu *cfi_shadow __read_mostly = NULL;
+
+static inline int ptr_to_shadow(const struct cfi_shadow *s, unsigned long ptr)
+{
+	unsigned long index;
+	unsigned long page = ptr >> PAGE_SHIFT;
+
+	if (unlikely(page < s->r.min_page))
+		return -1; /* Outside of module area */
+
+	index = page - s->r.min_page;
+
+	if (index >= SHADOW_SIZE)
+		return -1; /* Cannot be addressed with shadow */
+
+	return (int)index;
+}
+
+static inline unsigned long shadow_to_ptr(const struct cfi_shadow *s,
+	int index)
+{
+	BUG_ON(index < 0 || index >= SHADOW_SIZE);
+
+	if (unlikely(s->shadow[index] == SHADOW_INVALID))
+		return 0;
+
+	return (s->r.min_page + s->shadow[index]) << PAGE_SHIFT;
+}
+
+static inline unsigned long shadow_to_page(const struct cfi_shadow *s,
+	int index)
+{
+	BUG_ON(index < 0 || index >= SHADOW_SIZE);
+
+	return (s->r.min_page + index) << PAGE_SHIFT;
+}
+
+static void prepare_next_shadow(const struct cfi_shadow __rcu *prev,
+		struct cfi_shadow *next)
+{
+	int i, index, check;
+
+	/* Mark everything invalid */
+	memset(next->shadow, 0xFF, sizeof(next->shadow));
+
+	if (!prev)
+		return; /* No previous shadow */
+
+	/* If the base address didn't change, update is not needed */
+	if (prev->r.min_page == next->r.min_page) {
+		memcpy(next->shadow, prev->shadow, sizeof(next->shadow));
+		return;
+	}
+
+	/* Convert the previous shadow to the new address range */
+	for (i = 0; i < SHADOW_SIZE; ++i) {
+		if (prev->shadow[i] == SHADOW_INVALID)
+			continue;
+
+		index = ptr_to_shadow(next, shadow_to_page(prev, i));
+		if (index < 0)
+			continue;
+
+		check = ptr_to_shadow(next,
+				shadow_to_ptr(prev, prev->shadow[i]));
+		if (check < 0)
+			continue;
+
+		next->shadow[index] = (u16)check;
+	}
+}
+
+static void add_module_to_shadow(struct cfi_shadow *s, struct module *mod)
+{
+	unsigned long ptr;
+	unsigned long min_page_addr;
+	unsigned long max_page_addr;
+	unsigned long check = (unsigned long)mod->cfi_check;
+	int check_index = ptr_to_shadow(s, check);
+
+	BUG_ON((check & PAGE_MASK) != check); /* Must be page aligned */
+
+	if (check_index < 0)
+		return; /* Module not addressable with shadow */
+
+	min_page_addr = (unsigned long)mod->core_layout.base & PAGE_MASK;
+	max_page_addr = (unsigned long)mod->core_layout.base +
+				       mod->core_layout.text_size;
+	max_page_addr &= PAGE_MASK;
+
+	/* For each page, store the check function index in the shadow */
+	for (ptr = min_page_addr; ptr <= max_page_addr; ptr += PAGE_SIZE) {
+		int index = ptr_to_shadow(s, ptr);
+		if (index >= 0) {
+			/* Assume a page only contains code for one module */
+			BUG_ON(s->shadow[index] != SHADOW_INVALID);
+			s->shadow[index] = (u16)check_index;
+		}
+	}
+}
+
+static void remove_module_from_shadow(struct cfi_shadow *s, struct module *mod)
+{
+	unsigned long ptr;
+	unsigned long min_page_addr;
+	unsigned long max_page_addr;
+
+	min_page_addr = (unsigned long)mod->core_layout.base & PAGE_MASK;
+	max_page_addr = (unsigned long)mod->core_layout.base +
+				       mod->core_layout.text_size;
+	max_page_addr &= PAGE_MASK;
+
+	for (ptr = min_page_addr; ptr <= max_page_addr; ptr += PAGE_SIZE) {
+		int index = ptr_to_shadow(s, ptr);
+		if (index >= 0)
+			s->shadow[index] = SHADOW_INVALID;
+	}
+}
+
+typedef void (*update_shadow_fn)(struct cfi_shadow *, struct module *);
+
+static void update_shadow(struct module *mod, unsigned long min_addr,
+	unsigned long max_addr, update_shadow_fn fn)
+{
+	struct cfi_shadow *prev;
+	struct cfi_shadow *next = (struct cfi_shadow *)
+		__get_free_pages(GFP_KERNEL, SHADOW_ORDER);
+
+	BUG_ON(!next);
+
+	next->r.mod_min_addr = min_addr;
+	next->r.mod_max_addr = max_addr;
+	next->r.min_page = min_addr >> PAGE_SHIFT;
+	next->r.max_page = max_addr >> PAGE_SHIFT;
+
+	spin_lock(&shadow_update_lock);
+	prev = rcu_dereference_protected(cfi_shadow, 1);
+	prepare_next_shadow(prev, next);
+
+	fn(next, mod);
+	set_memory_ro((unsigned long)next, SHADOW_PAGES);
+	rcu_assign_pointer(cfi_shadow, next);
+
+	spin_unlock(&shadow_update_lock);
+	synchronize_rcu();
+
+	if (prev) {
+		set_memory_rw((unsigned long)prev, SHADOW_PAGES);
+		free_pages((unsigned long)prev, SHADOW_ORDER);
+	}
+}
+
+void cfi_module_add(struct module *mod, unsigned long min_addr,
+	unsigned long max_addr)
+{
+	update_shadow(mod, min_addr, max_addr, add_module_to_shadow);
+}
+EXPORT_SYMBOL(cfi_module_add);
+
+void cfi_module_remove(struct module *mod, unsigned long min_addr,
+	unsigned long max_addr)
+{
+	update_shadow(mod, min_addr, max_addr, remove_module_from_shadow);
+}
+EXPORT_SYMBOL(cfi_module_remove);
+
+static inline cfi_check_fn ptr_to_check_fn(const struct cfi_shadow __rcu *s,
+	unsigned long ptr)
+{
+	int index;
+
+	if (unlikely(!s))
+		return NULL; /* No shadow available */
+
+	if (ptr < s->r.mod_min_addr || ptr > s->r.mod_max_addr)
+		return NULL; /* Not in a mapped module */
+
+	index = ptr_to_shadow(s, ptr);
+	if (index < 0)
+		return NULL; /* Cannot be addressed with shadow */
+
+	return (cfi_check_fn)shadow_to_ptr(s, index);
+}
+#endif /* CONFIG_CFI_CLANG_SHADOW */
+
+static inline cfi_check_fn find_module_cfi_check(void *ptr)
+{
+	struct module *mod;
+
+	preempt_disable();
+	mod = __module_address((unsigned long)ptr);
+	preempt_enable();
+
+	if (mod)
+		return mod->cfi_check;
+
+	return CFI_CHECK_FN;
+}
+
+static inline cfi_check_fn find_cfi_check(void *ptr)
+{
+#ifdef CONFIG_CFI_CLANG_SHADOW
+	cfi_check_fn f;
+
+	if (!rcu_access_pointer(cfi_shadow))
+		return CFI_CHECK_FN; /* No loaded modules */
+
+	/* Look up the __cfi_check function to use */
+	rcu_read_lock();
+	f = ptr_to_check_fn(rcu_dereference(cfi_shadow), (unsigned long)ptr);
+	rcu_read_unlock();
+
+	if (f)
+		return f;
+
+	/*
+	 * Fall back to find_module_cfi_check, which works also for a larger
+	 * module address space, but is slower.
+	 */
+#endif /* CONFIG_CFI_CLANG_SHADOW */
+
+	return find_module_cfi_check(ptr);
+}
+
+void cfi_slowpath_handler(uint64_t id, void *ptr, void *diag)
+{
+	cfi_check_fn check = find_cfi_check(ptr);
+
+	if (likely(check))
+		check(id, ptr, diag);
+	else /* Don't allow unchecked modules */
+		handle_cfi_failure(ptr);
+}
+EXPORT_SYMBOL(cfi_slowpath_handler);
+#endif /* CONFIG_MODULES */
+
+void cfi_failure_handler(void *data, void *ptr, void *vtable)
+{
+	handle_cfi_failure(ptr);
+}
+EXPORT_SYMBOL(cfi_failure_handler);
+
+void __cfi_check_fail(void *data, void *ptr)
+{
+	handle_cfi_failure(ptr);
+}