8da32d526d
When CONFIG_CFI_PERMISSIVE is not set, ensure the third argument passed to __cfi_check from __cfi_slowpath is NULL to avoid an invalid memory access in __cfi_check_fail. __cfi_check_fail always traps anyway, but the error message will be less confusing with this patch. Note that kernels built with full LTO aren't affected as they always clear the argument before a __cfi_slowpath call. Later kernel versions are also not affected as they use -fno-sanitize-trap=cfi. Bug: 196763360 Change-Id: Ifa5b4e324737a3069f7a772dd9b392042ec8407e Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
353 lines
8.5 KiB
C
353 lines
8.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Clang Control Flow Integrity (CFI) error and slowpath handling.
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*
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* Copyright (C) 2019 Google LLC
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*/
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#include <linux/hardirq.h>
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#include <linux/kallsyms.h>
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#include <linux/module.h>
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#include <linux/mutex.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/vmalloc.h>
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#include <asm/cacheflush.h>
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#include <asm/set_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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if (IS_ENABLED(CONFIG_CFI_PERMISSIVE))
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WARN_RATELIMIT(1, "CFI failure (target: %pS):\n", ptr);
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else
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panic("CFI failure (target: %pS)\n", ptr);
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}
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#ifdef CONFIG_MODULES
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#ifdef CONFIG_CFI_CLANG_SHADOW
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/*
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* Index type. A 16-bit index can address at most (2^16)-2 pages (taking
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* into account SHADOW_INVALID), i.e. ~256M with 4k pages.
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*/
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typedef u16 shadow_t;
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#define SHADOW_INVALID ((shadow_t)~0UL)
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struct cfi_shadow {
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/* Page index for the beginning of the shadow */
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unsigned long base;
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/* An array of __cfi_check locations (as indices to the shadow) */
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shadow_t shadow[1];
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} __packed;
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/*
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* The shadow covers ~128M from the beginning of the module region. If
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* the region is larger, we fall back to __module_address for the rest.
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*/
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#define __SHADOW_RANGE (_UL(SZ_128M) >> PAGE_SHIFT)
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/* The in-memory size of struct cfi_shadow, always at least one page */
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#define __SHADOW_PAGES ((__SHADOW_RANGE * sizeof(shadow_t)) >> PAGE_SHIFT)
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#define SHADOW_PAGES max(1UL, __SHADOW_PAGES)
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#define SHADOW_SIZE (SHADOW_PAGES << PAGE_SHIFT)
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/* The actual size of the shadow array, minus metadata */
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#define SHADOW_ARR_SIZE (SHADOW_SIZE - offsetof(struct cfi_shadow, shadow))
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#define SHADOW_ARR_SLOTS (SHADOW_ARR_SIZE / sizeof(shadow_t))
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static DEFINE_MUTEX(shadow_update_lock);
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static struct cfi_shadow __rcu *cfi_shadow __read_mostly;
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/* Returns the index in the shadow for the given address */
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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->base))
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return -1; /* Outside of module area */
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index = page - s->base;
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if (index >= SHADOW_ARR_SLOTS)
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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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/* Returns the page address for an index in the shadow */
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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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if (unlikely(index < 0 || index >= SHADOW_ARR_SLOTS))
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return 0;
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return (s->base + index) << PAGE_SHIFT;
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}
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/* Returns the __cfi_check function address for the given shadow location */
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static inline unsigned long shadow_to_check_fn(const struct cfi_shadow *s,
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int index)
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{
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if (unlikely(index < 0 || index >= SHADOW_ARR_SLOTS))
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return 0;
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if (unlikely(s->shadow[index] == SHADOW_INVALID))
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return 0;
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/* __cfi_check is always page aligned */
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return (s->base + 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, SHADOW_ARR_SIZE);
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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, an update is not needed */
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if (prev->base == next->base) {
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memcpy(next->shadow, prev->shadow, SHADOW_ARR_SIZE);
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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_ARR_SLOTS; ++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_check_fn(prev, prev->shadow[i]));
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if (check < 0)
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continue;
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next->shadow[index] = (shadow_t)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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unsigned long min_addr, unsigned long max_addr)
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{
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int check_index;
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unsigned long check = (unsigned long)mod->cfi_check;
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unsigned long ptr;
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if (unlikely(!PAGE_ALIGNED(check))) {
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pr_warn("cfi: not using shadow for module %s\n", mod->name);
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return;
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}
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check_index = ptr_to_shadow(s, check);
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if (check_index < 0)
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return; /* Module not addressable with shadow */
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/* For each page, store the check function index in the shadow */
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for (ptr = min_addr; ptr <= max_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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/* Each page must only contain one module */
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WARN_ON_ONCE(s->shadow[index] != SHADOW_INVALID);
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s->shadow[index] = (shadow_t)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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unsigned long min_addr, unsigned long max_addr)
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{
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unsigned long ptr;
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for (ptr = min_addr; ptr <= max_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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unsigned long min_addr, unsigned long max_addr);
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static void update_shadow(struct module *mod, unsigned long base_addr,
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update_shadow_fn fn)
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{
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struct cfi_shadow *prev;
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struct cfi_shadow *next;
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unsigned long min_addr, max_addr;
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next = (struct cfi_shadow *)vmalloc(SHADOW_SIZE);
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WARN_ON(!next);
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mutex_lock(&shadow_update_lock);
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prev = rcu_dereference_protected(cfi_shadow,
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mutex_is_locked(&shadow_update_lock));
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if (next) {
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next->base = base_addr >> PAGE_SHIFT;
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prepare_next_shadow(prev, next);
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min_addr = (unsigned long)mod->core_layout.base;
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max_addr = min_addr + mod->core_layout.text_size;
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fn(next, mod, min_addr & PAGE_MASK, max_addr & PAGE_MASK);
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set_memory_ro((unsigned long)next, SHADOW_PAGES);
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}
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rcu_assign_pointer(cfi_shadow, next);
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mutex_unlock(&shadow_update_lock);
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synchronize_rcu_expedited();
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if (prev) {
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set_memory_rw((unsigned long)prev, SHADOW_PAGES);
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vfree(prev);
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}
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}
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void cfi_module_add(struct module *mod, unsigned long base_addr)
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{
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update_shadow(mod, base_addr, add_module_to_shadow);
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}
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void cfi_module_remove(struct module *mod, unsigned long base_addr)
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{
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update_shadow(mod, base_addr, remove_module_from_shadow);
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}
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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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if (unlikely(!s))
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return NULL; /* No shadow available */
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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_check_fn(s, index);
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}
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static inline cfi_check_fn __find_shadow_check_fn(unsigned long ptr)
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{
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cfi_check_fn fn;
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rcu_read_lock_sched_notrace();
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fn = ptr_to_check_fn(rcu_dereference_sched(cfi_shadow), ptr);
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rcu_read_unlock_sched_notrace();
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return fn;
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}
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#else /* !CONFIG_CFI_CLANG_SHADOW */
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static inline cfi_check_fn __find_shadow_check_fn(unsigned long ptr)
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{
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return NULL;
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}
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#endif /* CONFIG_CFI_CLANG_SHADOW */
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static inline cfi_check_fn __find_module_check_fn(unsigned long ptr)
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{
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cfi_check_fn fn = NULL;
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struct module *mod;
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rcu_read_lock_sched_notrace();
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mod = __module_address(ptr);
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if (mod)
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fn = mod->cfi_check;
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rcu_read_unlock_sched_notrace();
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return fn;
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}
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static inline cfi_check_fn find_check_fn(unsigned long ptr)
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{
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bool rcu;
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cfi_check_fn fn = NULL;
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/*
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* Indirect call checks can happen when RCU is not watching. Both
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* the shadow and __module_address use RCU, so we need to wake it
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* up before proceeding. Use rcu_nmi_enter/exit() as these calls
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* can happen anywhere.
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*/
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rcu = rcu_is_watching();
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if (!rcu)
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rcu_nmi_enter();
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if (IS_ENABLED(CONFIG_CFI_CLANG_SHADOW)) {
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fn = __find_shadow_check_fn(ptr);
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if (fn)
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goto out;
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}
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if (is_kernel_text(ptr)) {
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fn = __cfi_check;
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goto out;
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}
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fn = __find_module_check_fn(ptr);
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out:
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if (!rcu)
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rcu_nmi_exit();
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return fn;
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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 fn = find_check_fn((unsigned long)ptr);
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if (!IS_ENABLED(CONFIG_CFI_PERMISSIVE))
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diag = NULL;
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if (likely(fn))
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fn(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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#else /* !CONFIG_MODULES */
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void cfi_slowpath_handler(uint64_t id, void *ptr, void *diag)
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{
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handle_cfi_failure(ptr); /* No modules */
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}
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#endif /* CONFIG_MODULES */
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EXPORT_SYMBOL(cfi_slowpath_handler);
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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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