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/kernel/Makefile | 2 ++ arch/x86/kernel/cfi.c | 86 ++++++++++++++++++++++++++++++++++++++++++++++++ arch/x86/kernel/traps.c | 4 ++- 3 files changed, 91 insertions(+), 1 deletion(-) create mode 100644 arch/x86/kernel/cfi.c (limited to 'arch/x86/kernel') 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 v1.2.3-59-g8ed1b