diff --git a/Makefile b/Makefile index 3f0530ef8a35..111b2a92baee 100644 --- a/Makefile +++ b/Makefile @@ -882,6 +882,25 @@ KBUILD_CFLAGS += $(CC_FLAGS_LTO) export CC_FLAGS_LTO endif +ifdef CONFIG_CFI_CLANG +CC_FLAGS_CFI := -fsanitize=cfi \ + -fno-sanitize-cfi-canonical-jump-tables + +ifdef CONFIG_MODULES +CC_FLAGS_CFI += -fsanitize-cfi-cross-dso +endif + +ifdef CONFIG_CFI_PERMISSIVE +CC_FLAGS_CFI += -fsanitize-recover=cfi \ + -fno-sanitize-trap=cfi +endif + +# If LTO flags are filtered out, we must also filter out CFI. +CC_FLAGS_LTO += $(CC_FLAGS_CFI) +KBUILD_CFLAGS += $(CC_FLAGS_CFI) +export CC_FLAGS_CFI +endif + # arch Makefile may override CC so keep this after arch Makefile is included NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) diff --git a/arch/Kconfig b/arch/Kconfig index 12f11fcba9cd..5d862499ac02 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -602,6 +602,29 @@ config LTO_CLANG endchoice +config CFI_CLANG + bool "Use Clang's Control Flow Integrity (CFI)" + depends on LTO_CLANG && KALLSYMS + help + This option enables Clang's Control Flow Integrity (CFI), which adds + runtime checking for indirect function calls. + +config CFI_CLANG_SHADOW + bool "Use CFI shadow to speed up cross-module checks" + default y + depends on CFI_CLANG + help + If you select this option, the kernel builds a fast look-up table of + CFI check functions in loaded modules to reduce overhead. + +config CFI_PERMISSIVE + bool "Use CFI in permissive mode" + depends on CFI_CLANG + help + When selected, Control Flow Integrity (CFI) violations result in a + warning instead of a kernel panic. This option is useful for finding + CFI violations during development. + config HAVE_ARCH_WITHIN_STACK_FRAMES bool help diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 73a215a7d33f..2f2965fa00fe 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -71,6 +71,7 @@ */ #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) #define TEXT_MAIN .text .text.[0-9a-zA-Z_]* +#define TEXT_CFI_MAIN .text.[0-9a-zA-Z_]*.cfi #define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..LPBX* #define SDATA_MAIN .sdata .sdata.[0-9a-zA-Z_]* #define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]* @@ -78,6 +79,7 @@ #define SBSS_MAIN .sbss .sbss.[0-9a-zA-Z_]* #else #define TEXT_MAIN .text +#define TEXT_CFI_MAIN .text.cfi #define DATA_MAIN .data #define SDATA_MAIN .sdata #define RODATA_MAIN .rodata @@ -520,6 +522,7 @@ #define TEXT_TEXT \ ALIGN_FUNCTION(); \ *(.text.hot TEXT_MAIN .text.fixup .text.unlikely) \ + *(TEXT_CFI_MAIN) \ *(.text..refcount) \ *(.text..ftrace) \ *(.ref.text) \ diff --git a/include/linux/cfi.h b/include/linux/cfi.h new file mode 100644 index 000000000000..6ef37b35faaa --- /dev/null +++ b/include/linux/cfi.h @@ -0,0 +1,44 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Clang Control Flow Integrity (CFI) support. + * + * Copyright (C) 2019 Google LLC + */ +#ifndef _LINUX_CFI_H +#define _LINUX_CFI_H + +#include + +#ifdef CONFIG_CFI_CLANG +#ifdef CONFIG_MODULES + +typedef void (*cfi_check_fn)(uint64_t id, void *ptr, void *diag); + +/* Compiler-generated function in each module, and the kernel */ +#define CFI_CHECK_FN __cfi_check +#define CFI_CHECK_FN_NAME __stringify(CFI_CHECK_FN) + +extern void CFI_CHECK_FN(uint64_t id, void *ptr, void *diag); + +#ifdef CONFIG_CFI_CLANG_SHADOW +extern void cfi_module_add(struct module *mod, unsigned long min_addr, + unsigned long max_addr); + +extern void cfi_module_remove(struct module *mod, unsigned long min_addr, + unsigned long max_addr); +#else +static inline void cfi_module_add(struct module *mod, unsigned long min_addr, + unsigned long max_addr) +{ +} + +static inline void cfi_module_remove(struct module *mod, unsigned long min_addr, + unsigned long max_addr) +{ +} +#endif /* CONFIG_CFI_CLANG_SHADOW */ + +#endif /* CONFIG_MODULES */ +#endif /* CONFIG_CFI_CLANG */ + +#endif /* _LINUX_CFI_H */ diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index 5e97289e1e67..b7eea165e5f9 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -54,4 +54,7 @@ #define __norecordmcount \ __attribute__((__section__(".text..ftrace"))) #endif + + +#define __nocfi __attribute__((__no_sanitize__("cfi"))) #endif diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 48e7e3396656..a9baeafa207a 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -210,6 +210,10 @@ struct ftrace_likely_data { # define __norecordmcount #endif +#ifndef __nocfi +# define __nocfi +#endif + #ifndef asm_volatile_goto #define asm_volatile_goto(x...) asm goto(x) #endif diff --git a/include/linux/init.h b/include/linux/init.h index 0a16e48e6753..32633ea36f96 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -47,7 +47,7 @@ /* These are for everybody (although not all archs will actually discard it in modules) */ -#define __init __section(.init.text) __cold __latent_entropy __noinitretpoline +#define __init __section(.init.text) __cold __latent_entropy __noinitretpoline __nocfi #define __initdata __section(.init.data) #define __initconst __section(.init.rodata) #define __exitdata __section(.exit.data) diff --git a/include/linux/module.h b/include/linux/module.h index 6744ffe9a727..34027a495180 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -22,6 +22,7 @@ #include #include #include +#include #include #include @@ -365,6 +366,10 @@ struct module { const s32 *crcs; unsigned int num_syms; +#ifdef CONFIG_CFI_CLANG + cfi_check_fn cfi_check; +#endif + /* Kernel parameters. */ #ifdef CONFIG_SYSFS struct mutex param_lock; diff --git a/init/Kconfig b/init/Kconfig index fecbc6f6a2b4..7e9fa6466ff8 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -2219,7 +2219,7 @@ endif # MODULES config MODULES_TREE_LOOKUP def_bool y - depends on PERF_EVENTS || TRACING + depends on PERF_EVENTS || TRACING || CFI_CLANG config INIT_ALL_POSSIBLE bool diff --git a/kernel/Makefile b/kernel/Makefile index 313dbd44d576..ae0751315d29 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -35,6 +35,9 @@ CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) # cond_syscall is currently not LTO compatible CFLAGS_sys_ni.o = $(DISABLE_LTO) +# Don't instrument error handlers +CFLAGS_REMOVE_cfi.o := $(CC_FLAGS_CFI) + obj-y += sched/ obj-y += locking/ obj-y += power/ @@ -103,6 +106,7 @@ obj-$(CONFIG_IRQ_WORK) += irq_work.o obj-$(CONFIG_CPU_PM) += cpu_pm.o obj-$(CONFIG_BPF) += bpf/ obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o +obj-$(CONFIG_CFI_CLANG) += cfi.o obj-$(CONFIG_PERF_EVENTS) += events/ diff --git a/kernel/cfi.c b/kernel/cfi.c new file mode 100644 index 000000000000..05f589e24f68 --- /dev/null +++ b/kernel/cfi.c @@ -0,0 +1,307 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Clang Control Flow Integrity (CFI) error and slowpath handling. + * + * Copyright (C) 2019 Google LLC + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +/* Compiler-defined handler names */ +#ifdef CONFIG_CFI_PERMISSIVE +#define cfi_failure_handler __ubsan_handle_cfi_check_fail +#define cfi_slowpath_handler __cfi_slowpath_diag +#else /* enforcing */ +#define cfi_failure_handler __ubsan_handle_cfi_check_fail_abort +#define cfi_slowpath_handler __cfi_slowpath +#endif /* CONFIG_CFI_PERMISSIVE */ + +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 +struct shadow_range { + /* Module address range */ + unsigned long mod_min_addr; + unsigned long mod_max_addr; + /* Module page range */ + unsigned long min_page; + unsigned long max_page; +}; + +#define SHADOW_ORDER 2 +#define SHADOW_PAGES (1 << SHADOW_ORDER) +#define SHADOW_SIZE \ + ((SHADOW_PAGES * PAGE_SIZE - sizeof(struct shadow_range)) / sizeof(u16)) +#define SHADOW_INVALID 0xFFFF + +struct cfi_shadow { + /* Page range covered by the shadow */ + struct shadow_range r; + /* Page offsets to __cfi_check functions in modules */ + u16 shadow[SHADOW_SIZE]; +}; + +static DEFINE_MUTEX(shadow_update_lock); +static struct cfi_shadow __rcu *cfi_shadow __read_mostly; + +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->r.min_page)) + return -1; /* Outside of module area */ + + index = page - s->r.min_page; + + if (index >= SHADOW_SIZE) + return -1; /* Cannot be addressed with shadow */ + + return (int)index; +} + +static inline unsigned long shadow_to_ptr(const struct cfi_shadow *s, + int index) +{ + if (unlikely(index < 0 || index >= SHADOW_SIZE)) + return 0; + + if (unlikely(s->shadow[index] == SHADOW_INVALID)) + return 0; + + return (s->r.min_page + s->shadow[index]) << PAGE_SHIFT; +} + +static inline unsigned long shadow_to_page(const struct cfi_shadow *s, + int index) +{ + if (unlikely(index < 0 || index >= SHADOW_SIZE)) + return 0; + + return (s->r.min_page + 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, sizeof(next->shadow)); + + if (!prev) + return; /* No previous shadow */ + + /* If the base address didn't change, update is not needed */ + if (prev->r.min_page == next->r.min_page) { + memcpy(next->shadow, prev->shadow, sizeof(next->shadow)); + return; + } + + /* Convert the previous shadow to the new address range */ + for (i = 0; i < SHADOW_SIZE; ++i) { + if (prev->shadow[i] == SHADOW_INVALID) + continue; + + index = ptr_to_shadow(next, shadow_to_page(prev, i)); + if (index < 0) + continue; + + check = ptr_to_shadow(next, + shadow_to_ptr(prev, prev->shadow[i])); + if (check < 0) + continue; + + next->shadow[index] = (u16)check; + } +} + +static void add_module_to_shadow(struct cfi_shadow *s, struct module *mod) +{ + unsigned long ptr; + unsigned long min_page_addr; + unsigned long max_page_addr; + unsigned long check = (unsigned long)mod->cfi_check; + int check_index = ptr_to_shadow(s, check); + + if (unlikely((check & PAGE_MASK) != check)) + return; /* Must be page aligned */ + + if (check_index < 0) + return; /* Module not addressable with shadow */ + + min_page_addr = (unsigned long)mod->core_layout.base & PAGE_MASK; + max_page_addr = (unsigned long)mod->core_layout.base + + mod->core_layout.text_size; + max_page_addr &= PAGE_MASK; + + /* For each page, store the check function index in the shadow */ + for (ptr = min_page_addr; ptr <= max_page_addr; ptr += PAGE_SIZE) { + int index = ptr_to_shadow(s, ptr); + + if (index >= 0) { + /* Each page must only contain one module */ + WARN_ON(s->shadow[index] != SHADOW_INVALID); + s->shadow[index] = (u16)check_index; + } + } +} + +static void remove_module_from_shadow(struct cfi_shadow *s, struct module *mod) +{ + unsigned long ptr; + unsigned long min_page_addr; + unsigned long max_page_addr; + + min_page_addr = (unsigned long)mod->core_layout.base & PAGE_MASK; + max_page_addr = (unsigned long)mod->core_layout.base + + mod->core_layout.text_size; + max_page_addr &= PAGE_MASK; + + for (ptr = min_page_addr; ptr <= max_page_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 *); + +static void update_shadow(struct module *mod, unsigned long min_addr, + unsigned long max_addr, update_shadow_fn fn) +{ + struct cfi_shadow *prev; + struct cfi_shadow *next = (struct cfi_shadow *) + __get_free_pages(GFP_KERNEL, SHADOW_ORDER); + + next->r.mod_min_addr = min_addr; + next->r.mod_max_addr = max_addr; + next->r.min_page = min_addr >> PAGE_SHIFT; + next->r.max_page = max_addr >> PAGE_SHIFT; + + mutex_lock(&shadow_update_lock); + prev = rcu_dereference_protected(cfi_shadow, 1); + prepare_next_shadow(prev, next); + + fn(next, mod); + 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); + free_pages((unsigned long)prev, SHADOW_ORDER); + } +} + +void cfi_module_add(struct module *mod, unsigned long min_addr, + unsigned long max_addr) +{ + update_shadow(mod, min_addr, max_addr, add_module_to_shadow); +} +EXPORT_SYMBOL(cfi_module_add); + +void cfi_module_remove(struct module *mod, unsigned long min_addr, + unsigned long max_addr) +{ + update_shadow(mod, min_addr, max_addr, remove_module_from_shadow); +} +EXPORT_SYMBOL(cfi_module_remove); + +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 */ + + if (ptr < s->r.mod_min_addr || ptr > s->r.mod_max_addr) + return NULL; /* Not in a mapped module */ + + index = ptr_to_shadow(s, ptr); + if (index < 0) + return NULL; /* Cannot be addressed with shadow */ + + return (cfi_check_fn)shadow_to_ptr(s, index); +} +#endif /* CONFIG_CFI_CLANG_SHADOW */ + +static inline cfi_check_fn find_module_cfi_check(void *ptr) +{ + struct module *mod; + + preempt_disable(); + mod = __module_address((unsigned long)ptr); + preempt_enable(); + + if (mod) + return mod->cfi_check; + + return CFI_CHECK_FN; +} + +static inline cfi_check_fn find_cfi_check(void *ptr) +{ +#ifdef CONFIG_CFI_CLANG_SHADOW + cfi_check_fn f; + + if (!rcu_access_pointer(cfi_shadow)) + return CFI_CHECK_FN; /* No loaded modules */ + + /* Look up the __cfi_check function to use */ + rcu_read_lock(); + f = ptr_to_check_fn(rcu_dereference(cfi_shadow), (unsigned long)ptr); + rcu_read_unlock(); + + if (f) + return f; + + /* + * Fall back to find_module_cfi_check, which works also for a larger + * module address space, but is slower. + */ +#endif /* CONFIG_CFI_CLANG_SHADOW */ + + return find_module_cfi_check(ptr); +} + +void cfi_slowpath_handler(uint64_t id, void *ptr, void *diag) +{ + cfi_check_fn check = find_cfi_check(ptr); + + if (likely(check)) + check(id, ptr, diag); + else /* Don't allow unchecked modules */ + handle_cfi_failure(ptr); +} +EXPORT_SYMBOL(cfi_slowpath_handler); +#endif /* CONFIG_MODULES */ + +void cfi_failure_handler(void *data, void *ptr, void *vtable) +{ + handle_cfi_failure(ptr); +} +EXPORT_SYMBOL(cfi_failure_handler); + +void __cfi_check_fail(void *data, void *ptr) +{ + handle_cfi_failure(ptr); +} diff --git a/kernel/module.c b/kernel/module.c index ff2d7359a418..47f391bc9ca2 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -2179,6 +2179,8 @@ 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) { @@ -2218,6 +2220,9 @@ static void free_module(struct module *mod) synchronize_rcu(); 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); @@ -3469,6 +3474,8 @@ int __weak module_finalize(const Elf_Ehdr *hdr, return 0; } +static void cfi_init(struct module *mod); + static int post_relocation(struct module *mod, const struct load_info *info) { /* Sort exception table now relocations are done. */ @@ -3481,6 +3488,9 @@ static int post_relocation(struct module *mod, const struct load_info *info) /* Setup kallsyms-specific fields. */ add_kallsyms(mod, info); + /* Setup CFI for the module. */ + cfi_init(mod); + /* Arch-specific module finalizing. */ return module_finalize(info->hdr, info->sechdrs, mod); } @@ -4284,6 +4294,24 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, } #endif /* CONFIG_KALLSYMS */ +static void cfi_init(struct module *mod) +{ +#ifdef CONFIG_CFI_CLANG + rcu_read_lock(); + mod->cfi_check = (cfi_check_fn)find_kallsyms_symbol_value(mod, + CFI_CHECK_FN_NAME); + rcu_read_unlock(); + cfi_module_add(mod, module_addr_min, module_addr_max); +#endif +} + +static void cfi_cleanup(struct module *mod) +{ +#ifdef CONFIG_CFI_CLANG + cfi_module_remove(mod, module_addr_min, module_addr_max); +#endif +} + /* Maximum number of characters written by module_flags() */ #define MODULE_FLAGS_BUF_SIZE (TAINT_FLAGS_COUNT + 4)