From f143ff397a3f991e8b48542f77aad900845f436e Mon Sep 17 00:00:00 2001 From: Sami Tolvanen Date: Thu, 8 Sep 2022 14:54:43 -0700 Subject: treewide: Filter out CC_FLAGS_CFI In preparation for removing CC_FLAGS_CFI from CC_FLAGS_LTO, explicitly filter out CC_FLAGS_CFI in all the makefiles where we currently filter out CC_FLAGS_LTO. Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Tested-by: Kees Cook Tested-by: Nathan Chancellor Acked-by: Peter Zijlstra (Intel) Tested-by: Peter Zijlstra (Intel) Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220908215504.3686827-2-samitolvanen@google.com --- arch/x86/entry/vdso/Makefile | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'arch/x86') diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile index 12f6c4d714cd..381d3333b996 100644 --- a/arch/x86/entry/vdso/Makefile +++ b/arch/x86/entry/vdso/Makefile @@ -91,7 +91,7 @@ ifneq ($(RETPOLINE_VDSO_CFLAGS),) endif endif -$(vobjs): KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO) $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL) +$(vobjs): KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO) $(CC_FLAGS_CFI) $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL) $(vobjs): KBUILD_AFLAGS += -DBUILD_VDSO # @@ -153,6 +153,7 @@ KBUILD_CFLAGS_32 := $(filter-out $(RANDSTRUCT_CFLAGS),$(KBUILD_CFLAGS_32)) KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32)) KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32)) KBUILD_CFLAGS_32 := $(filter-out $(CC_FLAGS_LTO),$(KBUILD_CFLAGS_32)) +KBUILD_CFLAGS_32 := $(filter-out $(CC_FLAGS_CFI),$(KBUILD_CFLAGS_32)) KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic KBUILD_CFLAGS_32 += -fno-stack-protector KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls) -- cgit v1.2.3-70-g09d2 From ca7e10bff196f69a450b9072a7b757713d3bb2dd Mon Sep 17 00:00:00 2001 From: Sami Tolvanen Date: Thu, 8 Sep 2022 14:55:01 -0700 Subject: x86/tools/relocs: Ignore __kcfi_typeid_ relocations The compiler generates __kcfi_typeid_ symbols for annotating assembly functions with type information. These are constants that can be referenced in assembly code and are resolved by the linker. Ignore them in relocs. Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Tested-by: Kees Cook Tested-by: Nathan Chancellor Acked-by: Peter Zijlstra (Intel) Tested-by: Peter Zijlstra (Intel) Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220908215504.3686827-20-samitolvanen@google.com --- arch/x86/tools/relocs.c | 1 + 1 file changed, 1 insertion(+) (limited to 'arch/x86') diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c index e2c5b296120d..2925074b9a58 100644 --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -56,6 +56,7 @@ static const char * const sym_regex_kernel[S_NSYMTYPES] = { "^(xen_irq_disable_direct_reloc$|" "xen_save_fl_direct_reloc$|" "VDSO|" + "__kcfi_typeid_|" "__crc_)", /* -- cgit v1.2.3-70-g09d2 From ccace936eec7b805e1ab9268a6d163a00047b3a9 Mon Sep 17 00:00:00 2001 From: Sami Tolvanen Date: Thu, 8 Sep 2022 14:55:02 -0700 Subject: x86: Add types to indirectly called assembly functions With CONFIG_CFI_CLANG, assembly functions indirectly called from C code must be annotated with type identifiers to pass CFI checking. Define the __CFI_TYPE helper macro to match the compiler generated function preamble, and ensure SYM_TYPED_FUNC_START also emits ENDBR with IBT. Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Tested-by: Kees Cook Tested-by: Nathan Chancellor Acked-by: Peter Zijlstra (Intel) Tested-by: Peter Zijlstra (Intel) Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220908215504.3686827-21-samitolvanen@google.com --- arch/x86/crypto/blowfish-x86_64-asm_64.S | 5 +++-- arch/x86/include/asm/linkage.h | 12 ++++++++++++ arch/x86/lib/memcpy_64.S | 3 ++- 3 files changed, 17 insertions(+), 3 deletions(-) (limited to 'arch/x86') diff --git a/arch/x86/crypto/blowfish-x86_64-asm_64.S b/arch/x86/crypto/blowfish-x86_64-asm_64.S index 802d71582689..4a43e072d2d1 100644 --- a/arch/x86/crypto/blowfish-x86_64-asm_64.S +++ b/arch/x86/crypto/blowfish-x86_64-asm_64.S @@ -6,6 +6,7 @@ */ #include +#include .file "blowfish-x86_64-asm.S" .text @@ -141,7 +142,7 @@ SYM_FUNC_START(__blowfish_enc_blk) RET; SYM_FUNC_END(__blowfish_enc_blk) -SYM_FUNC_START(blowfish_dec_blk) +SYM_TYPED_FUNC_START(blowfish_dec_blk) /* input: * %rdi: ctx * %rsi: dst @@ -332,7 +333,7 @@ SYM_FUNC_START(__blowfish_enc_blk_4way) RET; SYM_FUNC_END(__blowfish_enc_blk_4way) -SYM_FUNC_START(blowfish_dec_blk_4way) +SYM_TYPED_FUNC_START(blowfish_dec_blk_4way) /* input: * %rdi: ctx * %rsi: dst diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h index 73ca20049835..f484d656d34e 100644 --- a/arch/x86/include/asm/linkage.h +++ b/arch/x86/include/asm/linkage.h @@ -43,6 +43,18 @@ #endif /* __ASSEMBLY__ */ +#define __CFI_TYPE(name) \ + SYM_START(__cfi_##name, SYM_L_LOCAL, SYM_A_NONE) \ + .fill 11, 1, 0x90 ASM_NL \ + .byte 0xb8 ASM_NL \ + .long __kcfi_typeid_##name ASM_NL \ + SYM_FUNC_END(__cfi_##name) + +/* SYM_TYPED_FUNC_START -- use for indirectly called globals, w/ CFI type */ +#define SYM_TYPED_FUNC_START(name) \ + SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \ + ENDBR + /* SYM_FUNC_START -- use for global functions */ #define SYM_FUNC_START(name) \ SYM_START(name, SYM_L_GLOBAL, SYM_A_ALIGN) \ diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S index d0d7b9bc6cad..dd8cd8831251 100644 --- a/arch/x86/lib/memcpy_64.S +++ b/arch/x86/lib/memcpy_64.S @@ -2,6 +2,7 @@ /* Copyright 2002 Andi Kleen */ #include +#include #include #include #include @@ -27,7 +28,7 @@ * Output: * rax original destination */ -SYM_FUNC_START(__memcpy) +SYM_TYPED_FUNC_START(__memcpy) ALTERNATIVE_2 "jmp memcpy_orig", "", X86_FEATURE_REP_GOOD, \ "jmp memcpy_erms", X86_FEATURE_ERMS -- cgit v1.2.3-70-g09d2 From a4b7a12c5594fe5e6ab2a5aa514a9ae3c0b85573 Mon Sep 17 00:00:00 2001 From: Sami Tolvanen Date: Thu, 8 Sep 2022 14:55:03 -0700 Subject: x86/purgatory: Disable CFI Disable CONFIG_CFI_CLANG for the stand-alone purgatory.ro. Signed-off-by: Sami Tolvanen Reviewed-by: Nick Desaulniers Reviewed-by: Kees Cook Tested-by: Nick Desaulniers Tested-by: Sedat Dilek Tested-by: Kees Cook Tested-by: Nathan Chancellor Acked-by: Peter Zijlstra (Intel) Tested-by: Peter Zijlstra (Intel) Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220908215504.3686827-22-samitolvanen@google.com --- arch/x86/purgatory/Makefile | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/x86') diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile index 31c634a22818..58a200dc762d 100644 --- a/arch/x86/purgatory/Makefile +++ b/arch/x86/purgatory/Makefile @@ -55,6 +55,10 @@ ifdef CONFIG_RETPOLINE PURGATORY_CFLAGS_REMOVE += $(RETPOLINE_CFLAGS) endif +ifdef CONFIG_CFI_CLANG +PURGATORY_CFLAGS_REMOVE += $(CC_FLAGS_CFI) +endif + CFLAGS_REMOVE_purgatory.o += $(PURGATORY_CFLAGS_REMOVE) CFLAGS_purgatory.o += $(PURGATORY_CFLAGS) -- cgit v1.2.3-70-g09d2 From 3c516f89e17e56b4738f05588e51267e295b5e63 Mon Sep 17 00:00:00 2001 From: Sami Tolvanen Date: Thu, 8 Sep 2022 14:55:04 -0700 Subject: x86: Add support for CONFIG_CFI_CLANG With CONFIG_CFI_CLANG, the compiler injects a type preamble immediately before each function and a check to validate the target function type before indirect calls: ; type preamble __cfi_function: mov , %eax function: ... ; indirect call check mov -,%r10d add -0x4(%r11),%r10d je .Ltmp1 ud2 .Ltmp1: call __x86_indirect_thunk_r11 Add error handling code for the ud2 traps emitted for the checks, and allow CONFIG_CFI_CLANG to be selected on x86_64. This produces the following oops on CFI failure (generated using lkdtm): [ 21.441706] CFI failure at lkdtm_indirect_call+0x16/0x20 [lkdtm] (target: lkdtm_increment_int+0x0/0x10 [lkdtm]; expected type: 0x7e0c52a) [ 21.444579] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI [ 21.445296] CPU: 0 PID: 132 Comm: sh Not tainted 5.19.0-rc8-00020-g9f27360e674c #1 [ 21.445296] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [ 21.445296] RIP: 0010:lkdtm_indirect_call+0x16/0x20 [lkdtm] [ 21.445296] Code: 52 1c c0 48 c7 c1 c5 50 1c c0 e9 25 48 2a cc 0f 1f 44 00 00 49 89 fb 48 c7 c7 50 b4 1c c0 41 ba 5b ad f3 81 45 03 53 f8 [ 21.445296] RSP: 0018:ffffa9f9c02ffdc0 EFLAGS: 00000292 [ 21.445296] RAX: 0000000000000027 RBX: ffffffffc01cb300 RCX: 385cbbd2e070a700 [ 21.445296] RDX: 0000000000000000 RSI: c0000000ffffdfff RDI: ffffffffc01cb450 [ 21.445296] RBP: 0000000000000006 R08: 0000000000000000 R09: ffffffff8d081610 [ 21.445296] R10: 00000000bcc90825 R11: ffffffffc01c2fc0 R12: 0000000000000000 [ 21.445296] R13: ffffa31b827a6000 R14: 0000000000000000 R15: 0000000000000002 [ 21.445296] FS: 00007f08b42216a0(0000) GS:ffffa31b9f400000(0000) knlGS:0000000000000000 [ 21.445296] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 21.445296] CR2: 0000000000c76678 CR3: 0000000001940000 CR4: 00000000000006f0 [ 21.445296] Call Trace: [ 21.445296] [ 21.445296] lkdtm_CFI_FORWARD_PROTO+0x30/0x50 [lkdtm] [ 21.445296] direct_entry+0x12d/0x140 [lkdtm] [ 21.445296] full_proxy_write+0x5d/0xb0 [ 21.445296] vfs_write+0x144/0x460 [ 21.445296] ? __x64_sys_wait4+0x5a/0xc0 [ 21.445296] ksys_write+0x69/0xd0 [ 21.445296] do_syscall_64+0x51/0xa0 [ 21.445296] entry_SYSCALL_64_after_hwframe+0x63/0xcd [ 21.445296] RIP: 0033:0x7f08b41a6fe1 [ 21.445296] Code: be 07 00 00 00 41 89 c0 e8 7e ff ff ff 44 89 c7 89 04 24 e8 91 c6 02 00 8b 04 24 48 83 c4 68 c3 48 63 ff b8 01 00 00 03 [ 21.445296] RSP: 002b:00007ffcdf65c2e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 [ 21.445296] RAX: ffffffffffffffda RBX: 00007f08b4221690 RCX: 00007f08b41a6fe1 [ 21.445296] RDX: 0000000000000012 RSI: 0000000000c738f0 RDI: 0000000000000001 [ 21.445296] RBP: 0000000000000001 R08: fefefefefefefeff R09: fefefefeffc5ff4e [ 21.445296] R10: 00007f08b42222b0 R11: 0000000000000246 R12: 0000000000c738f0 [ 21.445296] R13: 0000000000000012 R14: 00007ffcdf65c401 R15: 0000000000c70450 [ 21.445296] [ 21.445296] Modules linked in: lkdtm [ 21.445296] Dumping ftrace buffer: [ 21.445296] (ftrace buffer empty) [ 21.471442] ---[ end trace 0000000000000000 ]--- [ 21.471811] RIP: 0010:lkdtm_indirect_call+0x16/0x20 [lkdtm] [ 21.472467] Code: 52 1c c0 48 c7 c1 c5 50 1c c0 e9 25 48 2a cc 0f 1f 44 00 00 49 89 fb 48 c7 c7 50 b4 1c c0 41 ba 5b ad f3 81 45 03 53 f8 [ 21.474400] RSP: 0018:ffffa9f9c02ffdc0 EFLAGS: 00000292 [ 21.474735] RAX: 0000000000000027 RBX: ffffffffc01cb300 RCX: 385cbbd2e070a700 [ 21.475664] RDX: 0000000000000000 RSI: c0000000ffffdfff RDI: ffffffffc01cb450 [ 21.476471] RBP: 0000000000000006 R08: 0000000000000000 R09: ffffffff8d081610 [ 21.477127] R10: 00000000bcc90825 R11: ffffffffc01c2fc0 R12: 0000000000000000 [ 21.477959] R13: ffffa31b827a6000 R14: 0000000000000000 R15: 0000000000000002 [ 21.478657] FS: 00007f08b42216a0(0000) GS:ffffa31b9f400000(0000) knlGS:0000000000000000 [ 21.479577] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 21.480307] CR2: 0000000000c76678 CR3: 0000000001940000 CR4: 00000000000006f0 [ 21.481460] Kernel panic - not syncing: Fatal exception Signed-off-by: Sami Tolvanen Reviewed-by: Kees Cook Tested-by: Kees Cook Tested-by: Nathan Chancellor Acked-by: Peter Zijlstra (Intel) Tested-by: Peter Zijlstra (Intel) Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220908215504.3686827-23-samitolvanen@google.com --- arch/x86/Kconfig | 2 ++ arch/x86/include/asm/cfi.h | 22 ++++++++++++ arch/x86/kernel/Makefile | 2 ++ arch/x86/kernel/cfi.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++ arch/x86/kernel/traps.c | 4 ++- 5 files changed, 115 insertions(+), 1 deletion(-) create mode 100644 arch/x86/include/asm/cfi.h create mode 100644 arch/x86/kernel/cfi.c (limited to 'arch/x86') diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index f9920f1341c8..1fe6a83dac05 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -107,6 +107,8 @@ config X86 select ARCH_SUPPORTS_PAGE_TABLE_CHECK if X86_64 select ARCH_SUPPORTS_NUMA_BALANCING if X86_64 select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP if NR_CPUS <= 4096 + select ARCH_SUPPORTS_CFI_CLANG if X86_64 + select ARCH_USES_CFI_TRAPS if X86_64 && CFI_CLANG select ARCH_SUPPORTS_LTO_CLANG select ARCH_SUPPORTS_LTO_CLANG_THIN select ARCH_USE_BUILTIN_BSWAP diff --git a/arch/x86/include/asm/cfi.h b/arch/x86/include/asm/cfi.h new file mode 100644 index 000000000000..58dacd90daef --- /dev/null +++ b/arch/x86/include/asm/cfi.h @@ -0,0 +1,22 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_X86_CFI_H +#define _ASM_X86_CFI_H + +/* + * Clang Control Flow Integrity (CFI) support. + * + * Copyright (C) 2022 Google LLC + */ + +#include + +#ifdef CONFIG_CFI_CLANG +enum bug_trap_type handle_cfi_failure(struct pt_regs *regs); +#else +static inline enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) +{ + return BUG_TRAP_TYPE_NONE; +} +#endif /* CONFIG_CFI_CLANG */ + +#endif /* _ASM_X86_CFI_H */ 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 +#include +#include +#include + +/* + * 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 -, %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 #include #include +#include #ifdef CONFIG_X86_64 #include @@ -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; } -- cgit v1.2.3-70-g09d2