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Message-Id: <20220908215504.3686827-4-samitolvanen@google.com> Date: Thu, 8 Sep 2022 14:54:45 -0700 From: Sami Tolvanen <samitolvanen@...gle.com> To: linux-kernel@...r.kernel.org Cc: Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Joao Moreira <joao@...rdrivepizza.com>, Sedat Dilek <sedat.dilek@...il.com>, Steven Rostedt <rostedt@...dmis.org>, linux-hardening@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev, Sami Tolvanen <samitolvanen@...gle.com> Subject: [PATCH v5 03/22] 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@...gle.com> Reviewed-by: Kees Cook <keescook@...omium.org> Tested-by: Kees Cook <keescook@...omium.org> Tested-by: Nathan Chancellor <nathan@...nel.org> --- arch/Kconfig | 10 -- include/linux/cfi.h | 12 --- kernel/cfi.c | 236 +------------------------------------------ kernel/module/main.c | 15 --- 4 files changed, 1 insertion(+), 272 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index 5dbf11a5ba4e..5fd875e18c99 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -754,16 +754,6 @@ config CFI_CLANG https://clang.llvm.org/docs/ControlFlowIntegrity.html -config CFI_CLANG_SHADOW - bool "Use CFI shadow to speed up cross-module checks" - default y - depends on CFI_CLANG && MODULES - help - If you select this option, the kernel builds a fast look-up table of - CFI check functions in loaded modules to reduce performance overhead. - - If unsure, say Y. - config CFI_PERMISSIVE bool "Use CFI in permissive mode" depends on CFI_CLANG diff --git a/include/linux/cfi.h b/include/linux/cfi.h index c6dfc1ed0626..4ab51c067007 100644 --- a/include/linux/cfi.h +++ b/include/linux/cfi.h @@ -20,18 +20,6 @@ extern void __cfi_check(uint64_t id, void *ptr, void *diag); #define __CFI_ADDRESSABLE(fn, __attr) \ const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn -#ifdef CONFIG_CFI_CLANG_SHADOW - -extern void cfi_module_add(struct module *mod, unsigned long base_addr); -extern void cfi_module_remove(struct module *mod, unsigned long base_addr); - -#else - -static inline void cfi_module_add(struct module *mod, unsigned long base_addr) {} -static inline void cfi_module_remove(struct module *mod, unsigned long base_addr) {} - -#endif /* CONFIG_CFI_CLANG_SHADOW */ - #else /* !CONFIG_CFI_CLANG */ #ifdef CONFIG_X86_KERNEL_IBT diff --git a/kernel/cfi.c b/kernel/cfi.c index 2046276ee234..e8bc1b370edc 100644 --- a/kernel/cfi.c +++ b/kernel/cfi.c @@ -32,237 +32,6 @@ static inline void handle_cfi_failure(void *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_notrace(); - fn = ptr_to_check_fn(rcu_dereference_sched(cfi_shadow), ptr); - rcu_read_unlock_sched_notrace(); - - 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) { @@ -298,10 +67,7 @@ static inline cfi_check_fn find_check_fn(unsigned long ptr) ct_irq_enter(); } - if (IS_ENABLED(CONFIG_CFI_CLANG_SHADOW)) - fn = find_shadow_check_fn(ptr); - if (!fn) - fn = find_module_check_fn(ptr); + fn = find_module_check_fn(ptr); if (rcu_idle) { ct_irq_exit(); diff --git a/kernel/module/main.c b/kernel/module/main.c index a4e4d84b6f4e..0228f44b58e5 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -1144,8 +1144,6 @@ void __weak module_arch_freeing_init(struct module *mod) { } -static void cfi_cleanup(struct module *mod); - /* Free a module, remove from lists, etc. */ static void free_module(struct module *mod) { @@ -1190,9 +1188,6 @@ static void free_module(struct module *mod) mod->name); mutex_unlock(&module_mutex); - /* Clean up CFI for the module. */ - cfi_cleanup(mod); - /* This may be empty, but that's OK */ module_arch_freeing_init(mod); module_memfree(mod->init_layout.base); @@ -2875,7 +2870,6 @@ static int load_module(struct load_info *info, const char __user *uargs, synchronize_rcu(); kfree(mod->args); free_arch_cleanup: - cfi_cleanup(mod); module_arch_cleanup(mod); free_modinfo: free_modinfo(mod); @@ -2984,15 +2978,6 @@ static void cfi_init(struct module *mod) mod->exit = *exit; #endif rcu_read_unlock_sched(); - - cfi_module_add(mod, mod_tree.addr_min); -#endif -} - -static void cfi_cleanup(struct module *mod) -{ -#ifdef CONFIG_CFI_CLANG - cfi_module_remove(mod, mod_tree.addr_min); #endif } -- 2.37.2.789.g6183377224-goog
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