--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Clang Control Flow Integrity (CFI) error and slowpath handling.
+ *
+ * Copyright (C) 2021 Google LLC
+ */
+
+#include <linux/hardirq.h>
+#include <linux/kallsyms.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/printk.h>
+#include <linux/ratelimit.h>
+#include <linux/rcupdate.h>
+#include <linux/vmalloc.h>
+#include <asm/cacheflush.h>
+#include <asm/set_memory.h>
+
+/* Compiler-defined handler names */
+#ifdef CONFIG_CFI_PERMISSIVE
+#define cfi_failure_handler __ubsan_handle_cfi_check_fail
+#else
+#define cfi_failure_handler __ubsan_handle_cfi_check_fail_abort
+#endif
+
+static inline void handle_cfi_failure(void *ptr)
+{
+ if (IS_ENABLED(CONFIG_CFI_PERMISSIVE))
+ WARN_RATELIMIT(1, "CFI failure (target: %pS):\n", ptr);
+ else
+ panic("CFI failure (target: %pS)\n", ptr);
+}
+
+#ifdef CONFIG_MODULES
+#ifdef CONFIG_CFI_CLANG_SHADOW
+/*
+ * Index type. A 16-bit index can address at most (2^16)-2 pages (taking
+ * into account SHADOW_INVALID), i.e. ~256M with 4k pages.
+ */
+typedef u16 shadow_t;
+#define SHADOW_INVALID ((shadow_t)~0UL)
+
+struct cfi_shadow {
+ /* Page index for the beginning of the shadow */
+ unsigned long base;
+ /* An array of __cfi_check locations (as indices to the shadow) */
+ shadow_t shadow[1];
+} __packed;
+
+/*
+ * The shadow covers ~128M from the beginning of the module region. If
+ * the region is larger, we fall back to __module_address for the rest.
+ */
+#define __SHADOW_RANGE (_UL(SZ_128M) >> PAGE_SHIFT)
+
+/* The in-memory size of struct cfi_shadow, always at least one page */
+#define __SHADOW_PAGES ((__SHADOW_RANGE * sizeof(shadow_t)) >> PAGE_SHIFT)
+#define SHADOW_PAGES max(1UL, __SHADOW_PAGES)
+#define SHADOW_SIZE (SHADOW_PAGES << PAGE_SHIFT)
+
+/* The actual size of the shadow array, minus metadata */
+#define SHADOW_ARR_SIZE (SHADOW_SIZE - offsetof(struct cfi_shadow, shadow))
+#define SHADOW_ARR_SLOTS (SHADOW_ARR_SIZE / sizeof(shadow_t))
+
+static DEFINE_MUTEX(shadow_update_lock);
+static struct cfi_shadow __rcu *cfi_shadow __read_mostly;
+
+/* Returns the index in the shadow for the given address */
+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->base))
+ return -1; /* Outside of module area */
+
+ index = page - s->base;
+
+ if (index >= SHADOW_ARR_SLOTS)
+ return -1; /* Cannot be addressed with shadow */
+
+ return (int)index;
+}
+
+/* Returns the page address for an index in the shadow */
+static inline unsigned long shadow_to_ptr(const struct cfi_shadow *s,
+ int index)
+{
+ if (unlikely(index < 0 || index >= SHADOW_ARR_SLOTS))
+ return 0;
+
+ return (s->base + index) << PAGE_SHIFT;
+}
+
+/* Returns the __cfi_check function address for the given shadow location */
+static inline unsigned long shadow_to_check_fn(const struct cfi_shadow *s,
+ int index)
+{
+ if (unlikely(index < 0 || index >= SHADOW_ARR_SLOTS))
+ return 0;
+
+ if (unlikely(s->shadow[index] == SHADOW_INVALID))
+ return 0;
+
+ /* __cfi_check is always page aligned */
+ return (s->base + s->shadow[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, SHADOW_ARR_SIZE);
+
+ if (!prev)
+ return; /* No previous shadow */
+
+ /* If the base address didn't change, an update is not needed */
+ if (prev->base == next->base) {
+ memcpy(next->shadow, prev->shadow, SHADOW_ARR_SIZE);
+ return;
+ }
+
+ /* Convert the previous shadow to the new address range */
+ for (i = 0; i < SHADOW_ARR_SLOTS; ++i) {
+ if (prev->shadow[i] == SHADOW_INVALID)
+ continue;
+
+ index = ptr_to_shadow(next, shadow_to_ptr(prev, i));
+ if (index < 0)
+ continue;
+
+ check = ptr_to_shadow(next,
+ shadow_to_check_fn(prev, prev->shadow[i]));
+ if (check < 0)
+ continue;
+
+ next->shadow[index] = (shadow_t)check;
+ }
+}
+
+static void add_module_to_shadow(struct cfi_shadow *s, struct module *mod,
+ unsigned long min_addr, unsigned long max_addr)
+{
+ int check_index;
+ unsigned long check = (unsigned long)mod->cfi_check;
+ unsigned long ptr;
+
+ if (unlikely(!PAGE_ALIGNED(check))) {
+ pr_warn("cfi: not using shadow for module %s\n", mod->name);
+ return;
+ }
+
+ check_index = ptr_to_shadow(s, check);
+ if (check_index < 0)
+ return; /* Module not addressable with shadow */
+
+ /* For each page, store the check function index in the shadow */
+ for (ptr = min_addr; ptr <= max_addr; ptr += PAGE_SIZE) {
+ int index = ptr_to_shadow(s, ptr);
+
+ if (index >= 0) {
+ /* Each page must only contain one module */
+ WARN_ON_ONCE(s->shadow[index] != SHADOW_INVALID);
+ s->shadow[index] = (shadow_t)check_index;
+ }
+ }
+}
+
+static void remove_module_from_shadow(struct cfi_shadow *s, struct module *mod,
+ unsigned long min_addr, unsigned long max_addr)
+{
+ unsigned long ptr;
+
+ for (ptr = min_addr; ptr <= max_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 *,
+ unsigned long min_addr, unsigned long max_addr);
+
+static void update_shadow(struct module *mod, unsigned long base_addr,
+ update_shadow_fn fn)
+{
+ struct cfi_shadow *prev;
+ struct cfi_shadow *next;
+ unsigned long min_addr, max_addr;
+
+ next = vmalloc(SHADOW_SIZE);
+
+ mutex_lock(&shadow_update_lock);
+ prev = rcu_dereference_protected(cfi_shadow,
+ mutex_is_locked(&shadow_update_lock));
+
+ if (next) {
+ next->base = base_addr >> PAGE_SHIFT;
+ prepare_next_shadow(prev, next);
+
+ min_addr = (unsigned long)mod->core_layout.base;
+ max_addr = min_addr + mod->core_layout.text_size;
+ fn(next, mod, min_addr & PAGE_MASK, max_addr & PAGE_MASK);
+
+ set_memory_ro((unsigned long)next, SHADOW_PAGES);
+ }
+
+ rcu_assign_pointer(cfi_shadow, next);
+ mutex_unlock(&shadow_update_lock);
+ synchronize_rcu();
+
+ if (prev) {
+ set_memory_rw((unsigned long)prev, SHADOW_PAGES);
+ vfree(prev);
+ }
+}
+
+void cfi_module_add(struct module *mod, unsigned long base_addr)
+{
+ update_shadow(mod, base_addr, add_module_to_shadow);
+}
+
+void cfi_module_remove(struct module *mod, unsigned long base_addr)
+{
+ update_shadow(mod, base_addr, remove_module_from_shadow);
+}
+
+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 */
+
+ index = ptr_to_shadow(s, ptr);
+ if (index < 0)
+ return NULL; /* Cannot be addressed with shadow */
+
+ return (cfi_check_fn)shadow_to_check_fn(s, index);
+}
+
+static inline cfi_check_fn find_shadow_check_fn(unsigned long ptr)
+{
+ cfi_check_fn fn;
+
+ rcu_read_lock_sched();
+ fn = ptr_to_check_fn(rcu_dereference_sched(cfi_shadow), ptr);
+ rcu_read_unlock_sched();
+
+ return fn;
+}
+
+#else /* !CONFIG_CFI_CLANG_SHADOW */
+
+static inline cfi_check_fn find_shadow_check_fn(unsigned long ptr)
+{
+ return NULL;
+}
+
+#endif /* CONFIG_CFI_CLANG_SHADOW */
+
+static inline cfi_check_fn find_module_check_fn(unsigned long ptr)
+{
+ cfi_check_fn fn = NULL;
+ struct module *mod;
+
+ rcu_read_lock_sched();
+ mod = __module_address(ptr);
+ if (mod)
+ fn = mod->cfi_check;
+ rcu_read_unlock_sched();
+
+ return fn;
+}
+
+static inline cfi_check_fn find_check_fn(unsigned long ptr)
+{
+ cfi_check_fn fn = NULL;
+
+ if (is_kernel_text(ptr))
+ return __cfi_check;
+
+ /*
+ * Indirect call checks can happen when RCU is not watching. Both
+ * the shadow and __module_address use RCU, so we need to wake it
+ * up if necessary.
+ */
+ RCU_NONIDLE({
+ if (IS_ENABLED(CONFIG_CFI_CLANG_SHADOW))
+ fn = find_shadow_check_fn(ptr);
+
+ if (!fn)
+ fn = find_module_check_fn(ptr);
+ });
+
+ return fn;
+}
+
+void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag)
+{
+ cfi_check_fn fn = find_check_fn((unsigned long)ptr);
+
+ if (likely(fn))
+ fn(id, ptr, diag);
+ else /* Don't allow unchecked modules */
+ handle_cfi_failure(ptr);
+}
+EXPORT_SYMBOL(__cfi_slowpath_diag);
+
+#else /* !CONFIG_MODULES */
+
+void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag)
+{
+ handle_cfi_failure(ptr); /* No modules */
+}
+EXPORT_SYMBOL(__cfi_slowpath_diag);
+
+#endif /* CONFIG_MODULES */
+
+void cfi_failure_handler(void *data, void *ptr, void *vtable)
+{
+ handle_cfi_failure(ptr);
+}
+EXPORT_SYMBOL(cfi_failure_handler);
projects / users / dwmw2 / linux.git / commitdiff