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