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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 2022-09-08 14:54:47 -07:00 committed by Kees Cook
parent 92efda8eb1
commit 8924560094
9 changed files with 139 additions and 182 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
Makefile
View File

@ -921,18 +921,7 @@ 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

8
arch/Kconfig
View File

@ -738,11 +738,13 @@ 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
depends on CLANG_VERSION >= 140000
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

37
include/asm-generic/vmlinux.lds.h
View File

@ -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)

29
include/linux/cfi.h
View File

@ -2,17 +2,38 @@
/*
* 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 <linux/bug.h>
#include <linux/module.h>
#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, u32 type);
/* Compiler-generated function in each module, and the kernel */
extern void __cfi_check(uint64_t id, void *ptr, void *diag);
static inline enum bug_trap_type report_cfi_failure_noaddr(struct pt_regs *regs,
unsigned long addr)
{
return report_cfi_failure(regs, addr, NULL, 0);
}
#ifdef CONFIG_ARCH_USES_CFI_TRAPS
bool is_cfi_trap(unsigned long addr);
#endif
#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 */

14
include/linux/compiler-clang.h
View File

@ -66,17 +66,9 @@
# define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
#endif
#define __nocfi __attribute__((__no_sanitize__("cfi")))
#define __cficanonical __attribute__((__cfi_canonical_jump_table__))
#if defined(CONFIG_CFI_CLANG)
/*
* With CONFIG_CFI_CLANG, the compiler replaces function address
* references with the address of the function's CFI jump table
* entry. The function_nocfi macro always returns the address of the
* actual function instead.
*/
#define function_nocfi(x) __builtin_function_start(x)
#if __has_feature(kcfi)
/* Disable CFI checking inside a function. */
#define __nocfi __attribute__((__no_sanitize__("kcfi")))
#endif
/*

6
include/linux/module.h
View File

@ -27,7 +27,6 @@
#include <linux/tracepoint-defs.h>
#include <linux/srcu.h>
#include <linux/static_call_types.h>
#include <linux/cfi.h>
#include <linux/percpu.h>
#include <asm/module.h>
@ -387,8 +386,9 @@ struct module {
const s32 *crcs;
unsigned int num_syms;
#ifdef CONFIG_CFI_CLANG
cfi_check_fn cfi_check;
#ifdef CONFIG_ARCH_USES_CFI_TRAPS
s32 *kcfi_traps;
s32 *kcfi_traps_end;
#endif
/* Kernel parameters. */

156
kernel/cfi.c
View File

@ -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>
#include <linux/cfi.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)
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_ARCH_USES_CFI_TRAPS
static inline unsigned long trap_address(s32 *p)
{
return (unsigned long)((long)p + (long)*p);
}
static bool is_trap(unsigned long addr, s32 *start, s32 *end)
{
s32 *p;
for (p = start; p < end; ++p) {
if (trap_address(p) == addr)
return true;
}
return false;
}
#ifdef CONFIG_MODULES
static inline cfi_check_fn find_module_check_fn(unsigned long ptr)
/* Populates `kcfi_trap(_end)?` fields in `struct module`. */
void module_cfi_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
struct module *mod)
{
char *secstrings;
unsigned int i;
mod->kcfi_traps = NULL;
mod->kcfi_traps_end = NULL;
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;
mod->kcfi_traps = (s32 *)sechdrs[i].sh_addr;
mod->kcfi_traps_end = (s32 *)(sechdrs[i].sh_addr + sechdrs[i].sh_size);
break;
}
}
static bool is_module_cfi_trap(unsigned long addr)
{
cfi_check_fn fn = NULL;
struct module *mod;
bool found = false;
rcu_read_lock_sched_notrace();
mod = __module_address(ptr);
mod = __module_address(addr);
if (mod)
fn = mod->cfi_check;
found = is_trap(addr, mod->kcfi_traps, mod->kcfi_traps_end);
rcu_read_unlock_sched_notrace();
return fn;
return found;
}
static inline cfi_check_fn find_check_fn(unsigned long ptr)
#else /* CONFIG_MODULES */
static inline bool is_module_cfi_trap(unsigned long addr)
{
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();
return false;
}
fn = find_module_check_fn(ptr);
if (rcu_idle) {
ct_irq_exit();
local_irq_restore(flags);
}
return fn;
}
void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag)
{
cfi_check_fn fn = find_check_fn((unsigned long)ptr);
if (likely(fn))
fn(id, ptr, diag);
else /* Don't allow unchecked modules */
handle_cfi_failure(ptr);
}
EXPORT_SYMBOL(__cfi_slowpath_diag);
#else /* !CONFIG_MODULES */
void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag)
{
handle_cfi_failure(ptr); /* No modules */
}
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 */

35
kernel/module/main.c
View File

@ -53,6 +53,7 @@
#include <linux/bsearch.h>
#include <linux/dynamic_debug.h>
#include <linux/audit.h>
#include <linux/cfi.h>
#include <uapi/linux/module.h>
#include "internal.h"
@ -2597,8 +2598,9 @@ 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);
if (module_check_misalignment(mod))
goto out_misaligned;
@ -2660,8 +2662,6 @@ 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.
@ -2791,9 +2791,6 @@ 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)) {
@ -2955,32 +2952,6 @@ static inline int within(unsigned long addr, void *start, unsigned long size)
return ((void *)addr >= start && (void *)addr < start + size);
}
static void cfi_init(struct module *mod)
{
#ifdef CONFIG_CFI_CLANG
initcall_t *init;
#ifdef CONFIG_MODULE_UNLOAD
exitcall_t *exit;
#endif
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");
/* Fix init/exit functions to point to the CFI jump table */
if (init)
mod->init = *init;
#ifdef CONFIG_MODULE_UNLOAD
exit = (exitcall_t *)
find_kallsyms_symbol_value(mod, "__cfi_jt_cleanup_module");
if (exit)
mod->exit = *exit;
#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)
{

23
scripts/module.lds.S
View File

@ -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
}