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cfi: Remove CONFIG_CFI_CLANG_SHADOW
In preparation to switching to -fsanitize=kcfi, remove support for the CFI module shadow that will no longer be needed. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Tested-by: Kees Cook <keescook@chromium.org> Tested-by: Nathan Chancellor <nathan@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220908215504.3686827-4-samitolvanen@google.com
This commit is contained in:
Sami Tolvanen
Kees Cook
parent
d0f9562ee4
commit
9fca711582
10
arch/Kconfig
10
arch/Kconfig
@ -754,16 +754,6 @@ config CFI_CLANG
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https://clang.llvm.org/docs/ControlFlowIntegrity.html
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config CFI_CLANG_SHADOW
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bool "Use CFI shadow to speed up cross-module checks"
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default y
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depends on CFI_CLANG && MODULES
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help
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If you select this option, the kernel builds a fast look-up table of
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CFI check functions in loaded modules to reduce performance overhead.
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If unsure, say Y.
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config CFI_PERMISSIVE
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bool "Use CFI in permissive mode"
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depends on CFI_CLANG
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@ -20,18 +20,6 @@ extern void __cfi_check(uint64_t id, void *ptr, void *diag);
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#define __CFI_ADDRESSABLE(fn, __attr) \
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const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn
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#ifdef CONFIG_CFI_CLANG_SHADOW
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extern void cfi_module_add(struct module *mod, unsigned long base_addr);
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extern void cfi_module_remove(struct module *mod, unsigned long base_addr);
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#else
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static inline void cfi_module_add(struct module *mod, unsigned long base_addr) {}
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static inline void cfi_module_remove(struct module *mod, unsigned long base_addr) {}
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#endif /* CONFIG_CFI_CLANG_SHADOW */
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#else /* !CONFIG_CFI_CLANG */
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#ifdef CONFIG_X86_KERNEL_IBT
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236
kernel/cfi.c
236
kernel/cfi.c
@ -32,237 +32,6 @@ static inline void handle_cfi_failure(void *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 = vmalloc(SHADOW_SIZE);
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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();
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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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@ -298,10 +67,7 @@ static inline cfi_check_fn find_check_fn(unsigned long ptr)
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ct_irq_enter();
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}
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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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fn = find_module_check_fn(ptr);
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fn = find_module_check_fn(ptr);
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if (rcu_idle) {
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ct_irq_exit();
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@ -1144,8 +1144,6 @@ void __weak module_arch_freeing_init(struct module *mod)
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{
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}
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static void cfi_cleanup(struct module *mod);
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/* Free a module, remove from lists, etc. */
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static void free_module(struct module *mod)
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{
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@ -1190,9 +1188,6 @@ static void free_module(struct module *mod)
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mod->name);
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mutex_unlock(&module_mutex);
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/* Clean up CFI for the module. */
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cfi_cleanup(mod);
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/* This may be empty, but that's OK */
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module_arch_freeing_init(mod);
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module_memfree(mod->init_layout.base);
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@ -2875,7 +2870,6 @@ static int load_module(struct load_info *info, const char __user *uargs,
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synchronize_rcu();
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kfree(mod->args);
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free_arch_cleanup:
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cfi_cleanup(mod);
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module_arch_cleanup(mod);
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free_modinfo:
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free_modinfo(mod);
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@ -2984,15 +2978,6 @@ static void cfi_init(struct module *mod)
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mod->exit = *exit;
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#endif
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rcu_read_unlock_sched();
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cfi_module_add(mod, mod_tree.addr_min);
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#endif
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}
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static void cfi_cleanup(struct module *mod)
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{
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#ifdef CONFIG_CFI_CLANG
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cfi_module_remove(mod, mod_tree.addr_min);
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#endif
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}
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