diff options
author | Sami Tolvanen <samitolvanen@google.com> | 2022-09-09 00:54:47 +0300 |
---|---|---|
committer | Kees Cook <keescook@chromium.org> | 2022-09-26 20:13:13 +0300 |
commit | 89245600941e4e0f87d77f60ee269b5e61ef4e49 (patch) | |
tree | a0069b5bd625907cb854091e6dbbeed4964815b0 /kernel/cfi.c | |
parent | 92efda8eb15295a07f450828b2db14485bfc09c2 (diff) | |
download | linux-89245600941e4e0f87d77f60ee269b5e61ef4e49.tar.xz |
cfi: Switch to -fsanitize=kcfi
Switch from Clang's original forward-edge control-flow integrity
implementation to -fsanitize=kcfi, which is better suited for the
kernel, as it doesn't require LTO, doesn't use a jump table that
requires altering function references, and won't break cross-module
function address equality.
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/20220908215504.3686827-6-samitolvanen@google.com
Diffstat (limited to 'kernel/cfi.c')
-rw-r--r-- | kernel/cfi.c | 144 |
1 files changed, 70 insertions, 74 deletions
diff --git a/kernel/cfi.c b/kernel/cfi.c index e8bc1b370edc..08caad776717 100644 --- a/kernel/cfi.c +++ b/kernel/cfi.c @@ -1,105 +1,101 @@ // SPDX-License-Identifier: GPL-2.0 /* - * Clang Control Flow Integrity (CFI) error and slowpath handling. + * Clang Control Flow Integrity (CFI) error handling. * - * Copyright (C) 2021 Google LLC + * Copyright (C) 2022 Google LLC */ -#include <linux/hardirq.h> -#include <linux/kallsyms.h> -#include <linux/module.h> -#include <linux/mutex.h> -#include <linux/printk.h> -#include <linux/ratelimit.h> -#include <linux/rcupdate.h> -#include <linux/vmalloc.h> -#include <asm/cacheflush.h> -#include <asm/set_memory.h> - -/* Compiler-defined handler names */ -#ifdef CONFIG_CFI_PERMISSIVE -#define cfi_failure_handler __ubsan_handle_cfi_check_fail -#else -#define cfi_failure_handler __ubsan_handle_cfi_check_fail_abort -#endif - -static inline void handle_cfi_failure(void *ptr) +#include <linux/cfi.h> + +enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr, + unsigned long *target, u32 type) { - if (IS_ENABLED(CONFIG_CFI_PERMISSIVE)) - WARN_RATELIMIT(1, "CFI failure (target: %pS):\n", ptr); + if (target) + pr_err("CFI failure at %pS (target: %pS; expected type: 0x%08x)\n", + (void *)addr, (void *)*target, type); else - panic("CFI failure (target: %pS)\n", ptr); + pr_err("CFI failure at %pS (no target information)\n", + (void *)addr); + + if (IS_ENABLED(CONFIG_CFI_PERMISSIVE)) { + __warn(NULL, 0, (void *)addr, 0, regs, NULL); + return BUG_TRAP_TYPE_WARN; + } + + return BUG_TRAP_TYPE_BUG; } -#ifdef CONFIG_MODULES +#ifdef CONFIG_ARCH_USES_CFI_TRAPS +static inline unsigned long trap_address(s32 *p) +{ + return (unsigned long)((long)p + (long)*p); +} -static inline cfi_check_fn find_module_check_fn(unsigned long ptr) +static bool is_trap(unsigned long addr, s32 *start, s32 *end) { - cfi_check_fn fn = NULL; - struct module *mod; + s32 *p; - rcu_read_lock_sched_notrace(); - mod = __module_address(ptr); - if (mod) - fn = mod->cfi_check; - rcu_read_unlock_sched_notrace(); + for (p = start; p < end; ++p) { + if (trap_address(p) == addr) + return true; + } - return fn; + return false; } -static inline cfi_check_fn find_check_fn(unsigned long ptr) +#ifdef CONFIG_MODULES +/* Populates `kcfi_trap(_end)?` fields in `struct module`. */ +void module_cfi_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, + struct module *mod) { - cfi_check_fn fn = NULL; - unsigned long flags; - bool rcu_idle; - - if (is_kernel_text(ptr)) - return __cfi_check; - - /* - * Indirect call checks can happen when RCU is not watching. Both - * the shadow and __module_address use RCU, so we need to wake it - * up if necessary. - */ - rcu_idle = !rcu_is_watching(); - if (rcu_idle) { - local_irq_save(flags); - ct_irq_enter(); - } + char *secstrings; + unsigned int i; - fn = find_module_check_fn(ptr); + mod->kcfi_traps = NULL; + mod->kcfi_traps_end = NULL; - if (rcu_idle) { - ct_irq_exit(); - local_irq_restore(flags); - } + secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset; + + for (i = 1; i < hdr->e_shnum; i++) { + if (strcmp(secstrings + sechdrs[i].sh_name, "__kcfi_traps")) + continue; - return fn; + mod->kcfi_traps = (s32 *)sechdrs[i].sh_addr; + mod->kcfi_traps_end = (s32 *)(sechdrs[i].sh_addr + sechdrs[i].sh_size); + break; + } } -void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag) +static bool is_module_cfi_trap(unsigned long addr) { - cfi_check_fn fn = find_check_fn((unsigned long)ptr); + struct module *mod; + bool found = false; - if (likely(fn)) - fn(id, ptr, diag); - else /* Don't allow unchecked modules */ - handle_cfi_failure(ptr); -} -EXPORT_SYMBOL(__cfi_slowpath_diag); + rcu_read_lock_sched_notrace(); -#else /* !CONFIG_MODULES */ + mod = __module_address(addr); + if (mod) + found = is_trap(addr, mod->kcfi_traps, mod->kcfi_traps_end); -void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag) + rcu_read_unlock_sched_notrace(); + + return found; +} +#else /* CONFIG_MODULES */ +static inline bool is_module_cfi_trap(unsigned long addr) { - handle_cfi_failure(ptr); /* No modules */ + return false; } -EXPORT_SYMBOL(__cfi_slowpath_diag); - #endif /* CONFIG_MODULES */ -void cfi_failure_handler(void *data, void *ptr, void *vtable) +extern s32 __start___kcfi_traps[]; +extern s32 __stop___kcfi_traps[]; + +bool is_cfi_trap(unsigned long addr) { - handle_cfi_failure(ptr); + if (is_trap(addr, __start___kcfi_traps, __stop___kcfi_traps)) + return true; + + return is_module_cfi_trap(addr); } -EXPORT_SYMBOL(cfi_failure_handler); +#endif /* CONFIG_ARCH_USES_CFI_TRAPS */ |