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author | Linus Torvalds <torvalds@linux-foundation.org> | 2022-10-03 17:11:07 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-10-03 17:11:07 -0700 |
commit | 865dad2022c52ac6c5c9a87c5cec78a69f633fb6 (patch) | |
tree | 12cbd2fec8623d506d4a444129d68cddbd1c2223 /arch/x86/kernel | |
parent | Merge tag 'execve-v6.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux (diff) | |
parent | x86: Add support for CONFIG_CFI_CLANG (diff) | |
download | linux-dev-865dad2022c52ac6c5c9a87c5cec78a69f633fb6.tar.xz linux-dev-865dad2022c52ac6c5c9a87c5cec78a69f633fb6.zip |
Merge tag 'kcfi-v6.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull kcfi updates from Kees Cook:
"This replaces the prior support for Clang's standard Control Flow
Integrity (CFI) instrumentation, which has required a lot of special
conditions (e.g. LTO) and work-arounds.
The new implementation ("Kernel CFI") is specific to C, directly
designed for the Linux kernel, and takes advantage of architectural
features like x86's IBT. This series retains arm64 support and adds
x86 support.
GCC support is expected in the future[1], and additional "generic"
architectural support is expected soon[2].
Summary:
- treewide: Remove old CFI support details
- arm64: Replace Clang CFI support with Clang KCFI support
- x86: Introduce Clang KCFI support"
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107048 [1]
Link: https://github.com/samitolvanen/llvm-project/commits/kcfi_generic [2]
* tag 'kcfi-v6.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: (22 commits)
x86: Add support for CONFIG_CFI_CLANG
x86/purgatory: Disable CFI
x86: Add types to indirectly called assembly functions
x86/tools/relocs: Ignore __kcfi_typeid_ relocations
kallsyms: Drop CONFIG_CFI_CLANG workarounds
objtool: Disable CFI warnings
objtool: Preserve special st_shndx indexes in elf_update_symbol
treewide: Drop __cficanonical
treewide: Drop WARN_ON_FUNCTION_MISMATCH
treewide: Drop function_nocfi
init: Drop __nocfi from __init
arm64: Drop unneeded __nocfi attributes
arm64: Add CFI error handling
arm64: Add types to indirect called assembly functions
psci: Fix the function type for psci_initcall_t
lkdtm: Emit an indirect call for CFI tests
cfi: Add type helper macros
cfi: Switch to -fsanitize=kcfi
cfi: Drop __CFI_ADDRESSABLE
cfi: Remove CONFIG_CFI_CLANG_SHADOW
...
Diffstat (limited to 'arch/x86/kernel')
-rw-r--r-- | arch/x86/kernel/Makefile | 2 | ||||
-rw-r--r-- | arch/x86/kernel/cfi.c | 86 | ||||
-rw-r--r-- | arch/x86/kernel/traps.c | 4 |
3 files changed, 91 insertions, 1 deletions
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index a20a5ebfacd7..1286a73ebdbc 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -139,6 +139,8 @@ obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o obj-$(CONFIG_AMD_MEM_ENCRYPT) += sev.o +obj-$(CONFIG_CFI_CLANG) += cfi.o + ### # 64 bit specific files ifeq ($(CONFIG_X86_64),y) diff --git a/arch/x86/kernel/cfi.c b/arch/x86/kernel/cfi.c new file mode 100644 index 000000000000..8674a5c0c031 --- /dev/null +++ b/arch/x86/kernel/cfi.c @@ -0,0 +1,86 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Clang Control Flow Integrity (CFI) support. + * + * Copyright (C) 2022 Google LLC + */ +#include <asm/cfi.h> +#include <asm/insn.h> +#include <asm/insn-eval.h> +#include <linux/string.h> + +/* + * Returns the target address and the expected type when regs->ip points + * to a compiler-generated CFI trap. + */ +static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target, + u32 *type) +{ + char buffer[MAX_INSN_SIZE]; + struct insn insn; + int offset = 0; + + *target = *type = 0; + + /* + * The compiler generates the following instruction sequence + * for indirect call checks: + * + * movl -<id>, %r10d ; 6 bytes + * addl -4(%reg), %r10d ; 4 bytes + * je .Ltmp1 ; 2 bytes + * ud2 ; <- regs->ip + * .Ltmp1: + * + * We can decode the expected type and the target address from the + * movl/addl instructions. + */ + if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 12, MAX_INSN_SIZE)) + return false; + if (insn_decode_kernel(&insn, &buffer[offset])) + return false; + if (insn.opcode.value != 0xBA) + return false; + + *type = -(u32)insn.immediate.value; + + if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 6, MAX_INSN_SIZE)) + return false; + if (insn_decode_kernel(&insn, &buffer[offset])) + return false; + if (insn.opcode.value != 0x3) + return false; + + /* Read the target address from the register. */ + offset = insn_get_modrm_rm_off(&insn, regs); + if (offset < 0) + return false; + + *target = *(unsigned long *)((void *)regs + offset); + + return true; +} + +/* + * Checks if a ud2 trap is because of a CFI failure, and handles the trap + * if needed. Returns a bug_trap_type value similarly to report_bug. + */ +enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) +{ + unsigned long target; + u32 type; + + if (!is_cfi_trap(regs->ip)) + return BUG_TRAP_TYPE_NONE; + + if (!decode_cfi_insn(regs, &target, &type)) + return report_cfi_failure_noaddr(regs, regs->ip); + + return report_cfi_failure(regs, regs->ip, &target, type); +} + +/* + * Ensure that __kcfi_typeid_ symbols are emitted for functions that may + * not be indirectly called with all configurations. + */ +__ADDRESSABLE(__memcpy) diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index d62b2cb85cea..178015a820f0 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -63,6 +63,7 @@ #include <asm/insn-eval.h> #include <asm/vdso.h> #include <asm/tdx.h> +#include <asm/cfi.h> #ifdef CONFIG_X86_64 #include <asm/x86_init.h> @@ -313,7 +314,8 @@ static noinstr bool handle_bug(struct pt_regs *regs) */ if (regs->flags & X86_EFLAGS_IF) raw_local_irq_enable(); - if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) { + if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN || + handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) { regs->ip += LEN_UD2; handled = true; } |