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Fri, 13 May 2022 13:22:15 -0700 (PDT) Date: Fri, 13 May 2022 13:21:44 -0700 In-Reply-To: <20220513202159.1550547-1-samitolvanen@google.com> Message-Id: <20220513202159.1550547-7-samitolvanen@google.com> Mime-Version: 1.0 References: <20220513202159.1550547-1-samitolvanen@google.com> X-Developer-Key: i=samitolvanen@google.com; a=openpgp; fpr=35CCFB63B283D6D3AEB783944CB5F6848BBC56EE X-Developer-Signature: v=1; a=openpgp-sha256; l=15262; h=from:subject; bh=o6CdCuNcxPwKwpmkpv7p1X90CAdPdvaaWPEtZqzJ3XE=; b=owEB7QES/pANAwAKAUy19oSLvFbuAcsmYgBifr3j6rhd7VRsqD7zucXreXJ7ZaNf6DPaYMcLutG9 7vnfmlOJAbMEAAEKAB0WIQQ1zPtjsoPW0663g5RMtfaEi7xW7gUCYn694wAKCRBMtfaEi7xW7r0QC/ 97uOH7x5RKTU/aAHQLlxOmNegxtd2PtEXwOXGVEKW203D4f6n5MqdBdM2Jj6NLSMS2zVXhO1Ix6JpJ wTeaiv5+oMu5GTzWiYkYpDvT7RugGEiOdwW3lWmrX+/8B0G1XbIZyDkLykymeurzjZcG9L5tDgR8M/ jVIirG2M0l5jtzmMmkfqjH/KYcOHCxTwRs2HE0wpmb0SX2Ctpdymw8SuT+vzzGM2KsqQHYJK7Hzob7 bA+KuvgvhQgsgA3pvWOEa/nIQ1wAQTaRTsjs8UeV/Uokf6fNitmtiHztvm3oFpMvySBJQLK6fMjD6j aB+WZH+h5FgVTvUVQNkQHy+SZvgJZ1Wn5DgpfZ8Q0GpJbVLszH9dC2dp8j+GR7td5Z61OEJOxELkJl 4R1qr8PF8PdrxXEvDYZkcQig4q/1lsv834hPEbiZMk0Su5+XsWidHS8xX8cCa52ewu1zuR82hnQK2F us/l/jDOQgh5ZvSyIcOZ6nuHO4c6PRKyUK8gB/+FtSfgA= X-Mailer: git-send-email 2.36.0.550.gb090851708-goog Subject: [RFC PATCH v2 06/21] cfi: Switch to -fsanitize=kcfi From: Sami Tolvanen To: linux-kernel@vger.kernel.org Cc: Kees Cook , Josh Poimboeuf , Peter Zijlstra , x86@kernel.org, Catalin Marinas , Will Deacon , Mark Rutland , Nathan Chancellor , Nick Desaulniers , Joao Moreira , Sedat Dilek , Steven Rostedt , linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev, Sami Tolvanen X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220513_212230_826211_633A4789 X-CRM114-Status: GOOD ( 24.72 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 Reviewed-by: Kees Cook Tested-by: Kees Cook --- Makefile | 13 +-- arch/Kconfig | 11 ++- include/asm-generic/vmlinux.lds.h | 37 ++++----- include/linux/cfi.h | 35 +++++++-- include/linux/compiler-clang.h | 6 +- include/linux/module.h | 6 +- kernel/cfi.c | 126 ++++++++++++++---------------- kernel/module.c | 34 +------- scripts/module.lds.S | 23 +----- 9 files changed, 128 insertions(+), 163 deletions(-) diff --git a/Makefile b/Makefile index 2284d1ca2503..8439551954f1 100644 --- a/Makefile +++ b/Makefile @@ -915,18 +915,7 @@ export CC_FLAGS_LTO endif ifdef CONFIG_CFI_CLANG -CC_FLAGS_CFI := -fsanitize=cfi \ - -fsanitize-cfi-cross-dso \ - -fno-sanitize-cfi-canonical-jump-tables \ - -fno-sanitize-trap=cfi \ - -fno-sanitize-blacklist - -ifdef CONFIG_CFI_PERMISSIVE -CC_FLAGS_CFI += -fsanitize-recover=cfi -endif - -# If LTO flags are filtered out, we must also filter out CFI. -CC_FLAGS_LTO += $(CC_FLAGS_CFI) +CC_FLAGS_CFI := -fsanitize=kcfi KBUILD_CFLAGS += $(CC_FLAGS_CFI) export CC_FLAGS_CFI endif diff --git a/arch/Kconfig b/arch/Kconfig index 625db6376726..f179170cb422 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -720,14 +720,13 @@ config ARCH_SUPPORTS_CFI_CLANG An architecture should select this option if it can support Clang's Control-Flow Integrity (CFI) checking. +config ARCH_USES_CFI_TRAPS + bool + config CFI_CLANG bool "Use Clang's Control Flow Integrity (CFI)" - depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG - # Clang >= 12: - # - https://bugs.llvm.org/show_bug.cgi?id=46258 - # - https://bugs.llvm.org/show_bug.cgi?id=47479 - depends on CLANG_VERSION >= 120000 - select KALLSYMS + depends on ARCH_SUPPORTS_CFI_CLANG + depends on $(cc-option,-fsanitize=kcfi) help This option enables Clang’s forward-edge Control Flow Integrity (CFI) checking, where the compiler injects a runtime check to each diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 69138e9db787..fcb3c7146a43 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -421,6 +421,22 @@ __end_ro_after_init = .; #endif +/* + * .kcfi_traps contains a list KCFI trap locations. + */ +#ifndef KCFI_TRAPS +#ifdef CONFIG_ARCH_USES_CFI_TRAPS +#define KCFI_TRAPS \ + __kcfi_traps : AT(ADDR(__kcfi_traps) - LOAD_OFFSET) { \ + __start___kcfi_traps = .; \ + KEEP(*(.kcfi_traps)) \ + __stop___kcfi_traps = .; \ + } +#else +#define KCFI_TRAPS +#endif +#endif + /* * Read only Data */ @@ -529,6 +545,8 @@ __stop___modver = .; \ } \ \ + KCFI_TRAPS \ + \ RO_EXCEPTION_TABLE \ NOTES \ BTF \ @@ -537,21 +555,6 @@ __end_rodata = .; -/* - * .text..L.cfi.jumptable.* contain Control-Flow Integrity (CFI) - * jump table entries. - */ -#ifdef CONFIG_CFI_CLANG -#define TEXT_CFI_JT \ - . = ALIGN(PMD_SIZE); \ - __cfi_jt_start = .; \ - *(.text..L.cfi.jumptable .text..L.cfi.jumptable.*) \ - . = ALIGN(PMD_SIZE); \ - __cfi_jt_end = .; -#else -#define TEXT_CFI_JT -#endif - /* * Non-instrumentable text section */ @@ -579,7 +582,6 @@ *(.text..refcount) \ *(.ref.text) \ *(.text.asan.* .text.tsan.*) \ - TEXT_CFI_JT \ MEM_KEEP(init.text*) \ MEM_KEEP(exit.text*) \ @@ -1008,8 +1010,7 @@ * keep any .init_array.* sections. * https://bugs.llvm.org/show_bug.cgi?id=46478 */ -#if defined(CONFIG_GCOV_KERNEL) || defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN) || \ - defined(CONFIG_CFI_CLANG) +#if defined(CONFIG_GCOV_KERNEL) || defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN) # ifdef CONFIG_CONSTRUCTORS # define SANITIZER_DISCARDS \ *(.eh_frame) diff --git a/include/linux/cfi.h b/include/linux/cfi.h index 2cdbc0fbd0ab..655b8b10ac3d 100644 --- a/include/linux/cfi.h +++ b/include/linux/cfi.h @@ -2,17 +2,42 @@ /* * Clang Control Flow Integrity (CFI) support. * - * Copyright (C) 2021 Google LLC + * Copyright (C) 2022 Google LLC */ #ifndef _LINUX_CFI_H #define _LINUX_CFI_H +#include +#include + #ifdef CONFIG_CFI_CLANG -typedef void (*cfi_check_fn)(uint64_t id, void *ptr, void *diag); +enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr, + unsigned long target, unsigned long type); +#else +static inline enum bug_trap_type report_cfi_failure(struct pt_regs *regs, + unsigned long addr, + unsigned long target, + unsigned long type) +{ + return BUG_TRAP_TYPE_NONE; +} +#endif /* CONFIG_CFI_CLANG */ -/* Compiler-generated function in each module, and the kernel */ -extern void __cfi_check(uint64_t id, void *ptr, void *diag); +#ifdef CONFIG_ARCH_USES_CFI_TRAPS +bool is_cfi_trap(unsigned long addr); +#else +static inline bool is_cfi_trap(unsigned long addr) { return false; } +#endif /* CONFIG_ARCH_USES_CFI_TRAPS */ -#endif /* CONFIG_CFI_CLANG */ +#ifdef CONFIG_MODULES +#ifdef CONFIG_ARCH_USES_CFI_TRAPS +void module_cfi_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, + struct module *mod); +#else +static inline void module_cfi_finalize(const Elf_Ehdr *hdr, + const Elf_Shdr *sechdrs, + struct module *mod) {} +#endif /* CONFIG_ARCH_USES_CFI_TRAPS */ +#endif /* CONFIG_MODULES */ #endif /* _LINUX_CFI_H */ diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index babb1347148c..42e55579d649 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -66,8 +66,10 @@ # define __noscs __attribute__((__no_sanitize__("shadow-call-stack"))) #endif -#define __nocfi __attribute__((__no_sanitize__("cfi"))) -#define __cficanonical __attribute__((__cfi_canonical_jump_table__)) +#if __has_feature(kcfi) +/* Disable CFI checking inside a function. */ +#define __nocfi __attribute__((__no_sanitize__("kcfi"))) +#endif /* * Turn individual warnings and errors on and off locally, depending diff --git a/include/linux/module.h b/include/linux/module.h index 87857275c047..3b485834be74 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -27,7 +27,6 @@ #include #include #include -#include #include #include @@ -388,8 +387,9 @@ struct module { const s32 *crcs; unsigned int num_syms; -#ifdef CONFIG_CFI_CLANG - cfi_check_fn cfi_check; +#ifdef CONFIG_ARCH_USES_CFI_TRAPS + unsigned long *kcfi_traps; + unsigned long *kcfi_traps_end; #endif /* Kernel parameters. */ diff --git a/kernel/cfi.c b/kernel/cfi.c index 2cc0d01ea980..456d5eac082a 100644 --- a/kernel/cfi.c +++ b/kernel/cfi.c @@ -1,94 +1,86 @@ // 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 -#include -#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 -#else -#define cfi_failure_handler __ubsan_handle_cfi_check_fail_abort -#endif - -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 +#include -static inline cfi_check_fn find_module_check_fn(unsigned long ptr) +enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr, + unsigned long target, unsigned long type) { - cfi_check_fn fn = NULL; - struct module *mod; + pr_err("CFI failure at %pS (target: %pS; expected type: 0x%08x)\n", + (void *)addr, (void *)target, (u32)type); - rcu_read_lock_sched_notrace(); - mod = __module_address(ptr); - if (mod) - fn = mod->cfi_check; - rcu_read_unlock_sched_notrace(); + if (IS_ENABLED(CONFIG_CFI_PERMISSIVE)) { + __warn(NULL, 0, (void *)addr, 0, regs, NULL); + return BUG_TRAP_TYPE_WARN; + } - return fn; + return BUG_TRAP_TYPE_BUG; } -static inline cfi_check_fn find_check_fn(unsigned long ptr) +#ifdef CONFIG_ARCH_USES_CFI_TRAPS +#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; + char *secstrings; + unsigned int i; - if (is_kernel_text(ptr)) - return __cfi_check; + mod->kcfi_traps = NULL; + mod->kcfi_traps_end = NULL; - /* - * 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_NONIDLE({ - fn = find_module_check_fn(ptr); - }); + secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset; - return fn; + for (i = 1; i < hdr->e_shnum; i++) { + if (strcmp(secstrings + sechdrs[i].sh_name, "__kcfi_traps")) + continue; + + mod->kcfi_traps = (unsigned long *)sechdrs[i].sh_addr; + mod->kcfi_traps_end = (unsigned long *)(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); + bool found = false; + struct module *mod; + unsigned long *p; - 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) + for (p = mod->kcfi_traps; !found && p < mod->kcfi_traps_end; ++p) + found = (*p == addr); + + rcu_read_unlock_sched_notrace(); -void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag) + 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 unsigned long __start___kcfi_traps[]; +extern unsigned long __stop___kcfi_traps[]; + +bool is_cfi_trap(unsigned long addr) { - handle_cfi_failure(ptr); + unsigned long *p; + + for (p = __start___kcfi_traps; p < __stop___kcfi_traps; ++p) + if (*p == addr) + return true; + + return is_module_cfi_trap(addr); } -EXPORT_SYMBOL(cfi_failure_handler); +#endif /* CONFIG_ARCH_USES_CFI_TRAPS */ diff --git a/kernel/module.c b/kernel/module.c index 296fe02323e9..411ae8c358e6 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -57,6 +57,7 @@ #include #include #include +#include #include #include "module-internal.h" @@ -3871,8 +3872,9 @@ static int complete_formation(struct module *mod, struct load_info *info) if (err < 0) goto out; - /* This relies on module_mutex for list integrity. */ + /* These rely on module_mutex for list integrity. */ module_bug_finalize(info->hdr, info->sechdrs, mod); + module_cfi_finalize(info->hdr, info->sechdrs, mod); module_enable_ro(mod, false); module_enable_nx(mod); @@ -3928,8 +3930,6 @@ static int unknown_module_param_cb(char *param, char *val, const char *modname, return 0; } -static void cfi_init(struct module *mod); - /* * Allocate and load the module: note that size of section 0 is always * zero, and we rely on this for optional sections. @@ -4059,9 +4059,6 @@ static int load_module(struct load_info *info, const char __user *uargs, flush_module_icache(mod); - /* Setup CFI for the module. */ - cfi_init(mod); - /* Now copy in args */ mod->args = strndup_user(uargs, ~0UL >> 1); if (IS_ERR(mod->args)) { @@ -4502,31 +4499,6 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, #endif /* CONFIG_LIVEPATCH */ #endif /* CONFIG_KALLSYMS */ -static void cfi_init(struct module *mod) -{ -#ifdef CONFIG_CFI_CLANG - initcall_t *init; - exitcall_t *exit; - - rcu_read_lock_sched(); - mod->cfi_check = (cfi_check_fn) - find_kallsyms_symbol_value(mod, "__cfi_check"); - init = (initcall_t *) - find_kallsyms_symbol_value(mod, "__cfi_jt_init_module"); - exit = (exitcall_t *) - find_kallsyms_symbol_value(mod, "__cfi_jt_cleanup_module"); - rcu_read_unlock_sched(); - - /* Fix init/exit functions to point to the CFI jump table */ - if (init) - mod->init = *init; -#ifdef CONFIG_MODULE_UNLOAD - if (exit) - mod->exit = *exit; -#endif -#endif -} - /* Maximum number of characters written by module_flags() */ #define MODULE_FLAGS_BUF_SIZE (TAINT_FLAGS_COUNT + 4) diff --git a/scripts/module.lds.S b/scripts/module.lds.S index 1d0e1e4dc3d2..0708896139cc 100644 --- a/scripts/module.lds.S +++ b/scripts/module.lds.S @@ -3,20 +3,10 @@ * Archs are free to supply their own linker scripts. ld will * combine them automatically. */ -#ifdef CONFIG_CFI_CLANG -# include -# define ALIGN_CFI ALIGN(PAGE_SIZE) -# define SANITIZER_DISCARDS *(.eh_frame) -#else -# define ALIGN_CFI -# define SANITIZER_DISCARDS -#endif - SECTIONS { /DISCARD/ : { *(.discard) *(.discard.*) - SANITIZER_DISCARDS } __ksymtab 0 : { *(SORT(___ksymtab+*)) } @@ -31,6 +21,10 @@ SECTIONS { __patchable_function_entries : { *(__patchable_function_entries) } +#ifdef CONFIG_ARCH_USES_CFI_TRAPS + __kcfi_traps : { KEEP(*(.kcfi_traps)) } +#endif + #ifdef CONFIG_LTO_CLANG /* * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and @@ -51,15 +45,6 @@ SECTIONS { *(.rodata .rodata.[0-9a-zA-Z_]*) *(.rodata..L*) } - - /* - * With CONFIG_CFI_CLANG, we assume __cfi_check is at the beginning - * of the .text section, and is aligned to PAGE_SIZE. - */ - .text : ALIGN_CFI { - *(.text.__cfi_check) - *(.text .text.[0-9a-zA-Z_]* .text..L.cfi*) - } #endif }