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
This commit is contained in:
Sami Tolvanen
Kees Cook
parent
92efda8eb1
commit
8924560094
13
Makefile
13
Makefile
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@ -921,18 +921,7 @@ export CC_FLAGS_LTO
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endif
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ifdef CONFIG_CFI_CLANG
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CC_FLAGS_CFI := -fsanitize=cfi \
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-fsanitize-cfi-cross-dso \
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-fno-sanitize-cfi-canonical-jump-tables \
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-fno-sanitize-trap=cfi \
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-fno-sanitize-blacklist
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ifdef CONFIG_CFI_PERMISSIVE
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CC_FLAGS_CFI += -fsanitize-recover=cfi
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endif
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# If LTO flags are filtered out, we must also filter out CFI.
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CC_FLAGS_LTO += $(CC_FLAGS_CFI)
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CC_FLAGS_CFI := -fsanitize=kcfi
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KBUILD_CFLAGS += $(CC_FLAGS_CFI)
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export CC_FLAGS_CFI
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endif
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@ -738,11 +738,13 @@ config ARCH_SUPPORTS_CFI_CLANG
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An architecture should select this option if it can support Clang's
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Control-Flow Integrity (CFI) checking.
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config ARCH_USES_CFI_TRAPS
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bool
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config CFI_CLANG
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bool "Use Clang's Control Flow Integrity (CFI)"
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depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG
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depends on CLANG_VERSION >= 140000
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select KALLSYMS
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depends on ARCH_SUPPORTS_CFI_CLANG
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depends on $(cc-option,-fsanitize=kcfi)
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help
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This option enables Clang’s forward-edge Control Flow Integrity
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(CFI) checking, where the compiler injects a runtime check to each
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@ -421,6 +421,22 @@
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__end_ro_after_init = .;
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#endif
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/*
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* .kcfi_traps contains a list KCFI trap locations.
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*/
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#ifndef KCFI_TRAPS
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#ifdef CONFIG_ARCH_USES_CFI_TRAPS
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#define KCFI_TRAPS \
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__kcfi_traps : AT(ADDR(__kcfi_traps) - LOAD_OFFSET) { \
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__start___kcfi_traps = .; \
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KEEP(*(.kcfi_traps)) \
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__stop___kcfi_traps = .; \
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}
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#else
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#define KCFI_TRAPS
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#endif
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#endif
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/*
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* Read only Data
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*/
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@ -529,6 +545,8 @@
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__stop___modver = .; \
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} \
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\
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KCFI_TRAPS \
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\
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RO_EXCEPTION_TABLE \
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NOTES \
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BTF \
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@ -537,21 +555,6 @@
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__end_rodata = .;
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/*
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* .text..L.cfi.jumptable.* contain Control-Flow Integrity (CFI)
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* jump table entries.
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*/
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#ifdef CONFIG_CFI_CLANG
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#define TEXT_CFI_JT \
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. = ALIGN(PMD_SIZE); \
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__cfi_jt_start = .; \
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*(.text..L.cfi.jumptable .text..L.cfi.jumptable.*) \
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. = ALIGN(PMD_SIZE); \
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__cfi_jt_end = .;
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#else
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#define TEXT_CFI_JT
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#endif
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/*
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* Non-instrumentable text section
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*/
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@ -579,7 +582,6 @@
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*(.text..refcount) \
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*(.ref.text) \
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*(.text.asan.* .text.tsan.*) \
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TEXT_CFI_JT \
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MEM_KEEP(init.text*) \
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MEM_KEEP(exit.text*) \
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@ -1008,8 +1010,7 @@
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* keep any .init_array.* sections.
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* https://bugs.llvm.org/show_bug.cgi?id=46478
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*/
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#if defined(CONFIG_GCOV_KERNEL) || defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN) || \
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defined(CONFIG_CFI_CLANG)
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#if defined(CONFIG_GCOV_KERNEL) || defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KCSAN)
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# ifdef CONFIG_CONSTRUCTORS
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# define SANITIZER_DISCARDS \
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*(.eh_frame)
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@ -2,17 +2,38 @@
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/*
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* Clang Control Flow Integrity (CFI) support.
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*
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* Copyright (C) 2021 Google LLC
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* Copyright (C) 2022 Google LLC
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*/
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#ifndef _LINUX_CFI_H
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#define _LINUX_CFI_H
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#include <linux/bug.h>
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#include <linux/module.h>
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#ifdef CONFIG_CFI_CLANG
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typedef void (*cfi_check_fn)(uint64_t id, void *ptr, void *diag);
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enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
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unsigned long *target, u32 type);
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/* Compiler-generated function in each module, and the kernel */
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extern void __cfi_check(uint64_t id, void *ptr, void *diag);
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static inline enum bug_trap_type report_cfi_failure_noaddr(struct pt_regs *regs,
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unsigned long addr)
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{
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return report_cfi_failure(regs, addr, NULL, 0);
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}
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#ifdef CONFIG_ARCH_USES_CFI_TRAPS
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bool is_cfi_trap(unsigned long addr);
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#endif
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#endif /* CONFIG_CFI_CLANG */
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#ifdef CONFIG_MODULES
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#ifdef CONFIG_ARCH_USES_CFI_TRAPS
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void module_cfi_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
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struct module *mod);
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#else
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static inline void module_cfi_finalize(const Elf_Ehdr *hdr,
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const Elf_Shdr *sechdrs,
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struct module *mod) {}
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#endif /* CONFIG_ARCH_USES_CFI_TRAPS */
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#endif /* CONFIG_MODULES */
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#endif /* _LINUX_CFI_H */
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@ -66,17 +66,9 @@
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# define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
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#endif
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#define __nocfi __attribute__((__no_sanitize__("cfi")))
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#define __cficanonical __attribute__((__cfi_canonical_jump_table__))
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#if defined(CONFIG_CFI_CLANG)
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/*
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* With CONFIG_CFI_CLANG, the compiler replaces function address
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* references with the address of the function's CFI jump table
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* entry. The function_nocfi macro always returns the address of the
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* actual function instead.
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*/
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#define function_nocfi(x) __builtin_function_start(x)
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#if __has_feature(kcfi)
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/* Disable CFI checking inside a function. */
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#define __nocfi __attribute__((__no_sanitize__("kcfi")))
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#endif
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/*
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@ -27,7 +27,6 @@
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#include <linux/tracepoint-defs.h>
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#include <linux/srcu.h>
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#include <linux/static_call_types.h>
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#include <linux/cfi.h>
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#include <linux/percpu.h>
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#include <asm/module.h>
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@ -387,8 +386,9 @@ struct module {
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const s32 *crcs;
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unsigned int num_syms;
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#ifdef CONFIG_CFI_CLANG
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cfi_check_fn cfi_check;
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#ifdef CONFIG_ARCH_USES_CFI_TRAPS
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s32 *kcfi_traps;
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s32 *kcfi_traps_end;
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#endif
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/* Kernel parameters. */
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156
kernel/cfi.c
156
kernel/cfi.c
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@ -1,105 +1,101 @@
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Clang Control Flow Integrity (CFI) error and slowpath handling.
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* Clang Control Flow Integrity (CFI) error handling.
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*
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* Copyright (C) 2021 Google LLC
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* Copyright (C) 2022 Google LLC
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*/
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#include <linux/hardirq.h>
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#include <linux/kallsyms.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/printk.h>
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#include <linux/ratelimit.h>
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#include <linux/rcupdate.h>
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#include <linux/vmalloc.h>
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#include <asm/cacheflush.h>
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#include <asm/set_memory.h>
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#include <linux/cfi.h>
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/* Compiler-defined handler names */
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#ifdef CONFIG_CFI_PERMISSIVE
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#define cfi_failure_handler __ubsan_handle_cfi_check_fail
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#else
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#define cfi_failure_handler __ubsan_handle_cfi_check_fail_abort
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#endif
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static inline void handle_cfi_failure(void *ptr)
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enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
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unsigned long *target, u32 type)
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{
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if (IS_ENABLED(CONFIG_CFI_PERMISSIVE))
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WARN_RATELIMIT(1, "CFI failure (target: %pS):\n", ptr);
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if (target)
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pr_err("CFI failure at %pS (target: %pS; expected type: 0x%08x)\n",
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(void *)addr, (void *)*target, type);
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else
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panic("CFI failure (target: %pS)\n", ptr);
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pr_err("CFI failure at %pS (no target information)\n",
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(void *)addr);
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if (IS_ENABLED(CONFIG_CFI_PERMISSIVE)) {
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__warn(NULL, 0, (void *)addr, 0, regs, NULL);
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return BUG_TRAP_TYPE_WARN;
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}
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return BUG_TRAP_TYPE_BUG;
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}
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#ifdef CONFIG_ARCH_USES_CFI_TRAPS
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static inline unsigned long trap_address(s32 *p)
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{
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return (unsigned long)((long)p + (long)*p);
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}
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static bool is_trap(unsigned long addr, s32 *start, s32 *end)
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{
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s32 *p;
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for (p = start; p < end; ++p) {
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if (trap_address(p) == addr)
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return true;
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}
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return false;
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}
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#ifdef CONFIG_MODULES
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static inline cfi_check_fn find_module_check_fn(unsigned long ptr)
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/* Populates `kcfi_trap(_end)?` fields in `struct module`. */
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void module_cfi_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
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struct module *mod)
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{
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char *secstrings;
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unsigned int i;
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mod->kcfi_traps = NULL;
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mod->kcfi_traps_end = NULL;
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secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
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for (i = 1; i < hdr->e_shnum; i++) {
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if (strcmp(secstrings + sechdrs[i].sh_name, "__kcfi_traps"))
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continue;
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mod->kcfi_traps = (s32 *)sechdrs[i].sh_addr;
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mod->kcfi_traps_end = (s32 *)(sechdrs[i].sh_addr + sechdrs[i].sh_size);
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break;
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}
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}
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static bool is_module_cfi_trap(unsigned long addr)
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{
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cfi_check_fn fn = NULL;
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struct module *mod;
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bool found = false;
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rcu_read_lock_sched_notrace();
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mod = __module_address(ptr);
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mod = __module_address(addr);
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if (mod)
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fn = mod->cfi_check;
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found = is_trap(addr, mod->kcfi_traps, mod->kcfi_traps_end);
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rcu_read_unlock_sched_notrace();
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return fn;
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return found;
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}
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static inline cfi_check_fn find_check_fn(unsigned long ptr)
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#else /* CONFIG_MODULES */
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static inline bool is_module_cfi_trap(unsigned long addr)
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{
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cfi_check_fn fn = NULL;
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unsigned long flags;
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bool rcu_idle;
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if (is_kernel_text(ptr))
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return __cfi_check;
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/*
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* Indirect call checks can happen when RCU is not watching. Both
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* the shadow and __module_address use RCU, so we need to wake it
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* up if necessary.
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*/
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rcu_idle = !rcu_is_watching();
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if (rcu_idle) {
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local_irq_save(flags);
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ct_irq_enter();
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}
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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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local_irq_restore(flags);
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}
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return fn;
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return false;
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}
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void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag)
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{
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cfi_check_fn fn = find_check_fn((unsigned long)ptr);
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if (likely(fn))
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fn(id, ptr, diag);
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else /* Don't allow unchecked modules */
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handle_cfi_failure(ptr);
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}
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EXPORT_SYMBOL(__cfi_slowpath_diag);
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#else /* !CONFIG_MODULES */
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void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag)
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{
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handle_cfi_failure(ptr); /* No modules */
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}
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EXPORT_SYMBOL(__cfi_slowpath_diag);
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#endif /* CONFIG_MODULES */
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void cfi_failure_handler(void *data, void *ptr, void *vtable)
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extern s32 __start___kcfi_traps[];
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extern s32 __stop___kcfi_traps[];
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bool is_cfi_trap(unsigned long addr)
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{
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handle_cfi_failure(ptr);
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if (is_trap(addr, __start___kcfi_traps, __stop___kcfi_traps))
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return true;
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return is_module_cfi_trap(addr);
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}
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EXPORT_SYMBOL(cfi_failure_handler);
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#endif /* CONFIG_ARCH_USES_CFI_TRAPS */
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|
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@ -53,6 +53,7 @@
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#include <linux/bsearch.h>
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#include <linux/dynamic_debug.h>
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#include <linux/audit.h>
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#include <linux/cfi.h>
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#include <uapi/linux/module.h>
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#include "internal.h"
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@ -2597,8 +2598,9 @@ static int complete_formation(struct module *mod, struct load_info *info)
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if (err < 0)
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goto out;
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/* This relies on module_mutex for list integrity. */
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/* These rely on module_mutex for list integrity. */
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module_bug_finalize(info->hdr, info->sechdrs, mod);
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module_cfi_finalize(info->hdr, info->sechdrs, mod);
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if (module_check_misalignment(mod))
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goto out_misaligned;
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@ -2660,8 +2662,6 @@ static int unknown_module_param_cb(char *param, char *val, const char *modname,
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return 0;
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}
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static void cfi_init(struct module *mod);
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/*
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* Allocate and load the module: note that size of section 0 is always
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* zero, and we rely on this for optional sections.
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|
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@ -2791,9 +2791,6 @@ static int load_module(struct load_info *info, const char __user *uargs,
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flush_module_icache(mod);
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/* Setup CFI for the module. */
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cfi_init(mod);
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/* Now copy in args */
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mod->args = strndup_user(uargs, ~0UL >> 1);
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if (IS_ERR(mod->args)) {
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|
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@ -2955,32 +2952,6 @@ static inline int within(unsigned long addr, void *start, unsigned long size)
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return ((void *)addr >= start && (void *)addr < start + size);
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}
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|
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static void cfi_init(struct module *mod)
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{
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#ifdef CONFIG_CFI_CLANG
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initcall_t *init;
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#ifdef CONFIG_MODULE_UNLOAD
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exitcall_t *exit;
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#endif
|
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rcu_read_lock_sched();
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mod->cfi_check = (cfi_check_fn)
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find_kallsyms_symbol_value(mod, "__cfi_check");
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init = (initcall_t *)
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find_kallsyms_symbol_value(mod, "__cfi_jt_init_module");
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/* Fix init/exit functions to point to the CFI jump table */
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if (init)
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mod->init = *init;
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#ifdef CONFIG_MODULE_UNLOAD
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exit = (exitcall_t *)
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find_kallsyms_symbol_value(mod, "__cfi_jt_cleanup_module");
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if (exit)
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mod->exit = *exit;
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#endif
|
||||
rcu_read_unlock_sched();
|
||||
#endif
|
||||
}
|
||||
|
||||
/* Keep in sync with MODULE_FLAGS_BUF_SIZE !!! */
|
||||
char *module_flags(struct module *mod, char *buf, bool show_state)
|
||||
{
|
||||
|
|
|
|||
|
|
@ -3,20 +3,10 @@
|
|||
* Archs are free to supply their own linker scripts. ld will
|
||||
* combine them automatically.
|
||||
*/
|
||||
#ifdef CONFIG_CFI_CLANG
|
||||
# include <asm/page.h>
|
||||
# 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+*)) }
|
||||
|
|
@ -33,6 +23,10 @@ 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
|
||||
|
|
@ -53,15 +47,6 @@ 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
|
||||
}
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue