From: Masami Hiramatsu Date: Tue, 11 Jul 2023 01:50:58 +0000 (+0900) Subject: x86/kprobes: Prohibit probing on compiler generated CFI checking code X-Git-Tag: v6.6.7~2059^2 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=b65413768abd27a55af74945aec58127a52b30a8;p=platform%2Fkernel%2Flinux-starfive.git x86/kprobes: Prohibit probing on compiler generated CFI checking code Prohibit probing on the compiler generated CFI typeid checking code because it is used for decoding typeid when CFI error happens. The compiler generates the following instruction sequence for indirect call checks on x86;   movl -, %r10d ; 6 bytes addl -4(%reg), %r10d ; 4 bytes je .Ltmp1 ; 2 bytes ud2 ; <- regs->ip And handle_cfi_failure() decodes these instructions (movl and addl) for the typeid and the target address. Thus if we put a kprobe on those instructions, the decode will fail and report a wrong typeid and target address. Signed-off-by: Masami Hiramatsu (Google) Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/168904025785.116016.12766408611437534723.stgit@devnote2 --- diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c index f7f6042..e8babeb 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -45,6 +45,7 @@ #include #include #include +#include #include #include @@ -293,7 +294,40 @@ static int can_probe(unsigned long paddr) #endif addr += insn.length; } + if (IS_ENABLED(CONFIG_CFI_CLANG)) { + /* + * The compiler generates the following instruction sequence + * for indirect call checks and cfi.c decodes this; + * + *  movl -, %r10d ; 6 bytes + * addl -4(%reg), %r10d ; 4 bytes + * je .Ltmp1 ; 2 bytes + * ud2 ; <- regs->ip + * .Ltmp1: + * + * Also, these movl and addl are used for showing expected + * type. So those must not be touched. + */ + __addr = recover_probed_instruction(buf, addr); + if (!__addr) + return 0; + + if (insn_decode_kernel(&insn, (void *)__addr) < 0) + return 0; + + if (insn.opcode.value == 0xBA) + offset = 12; + else if (insn.opcode.value == 0x3) + offset = 6; + else + goto out; + + /* This movl/addl is used for decoding CFI. */ + if (is_cfi_trap(addr + offset)) + return 0; + } +out: return (addr == paddr); } diff --git a/include/linux/cfi.h b/include/linux/cfi.h index 5e134f4..3552ec8 100644 --- a/include/linux/cfi.h +++ b/include/linux/cfi.h @@ -19,11 +19,13 @@ static inline enum bug_trap_type report_cfi_failure_noaddr(struct pt_regs *regs, { return report_cfi_failure(regs, addr, NULL, 0); } +#endif /* CONFIG_CFI_CLANG */ #ifdef CONFIG_ARCH_USES_CFI_TRAPS bool is_cfi_trap(unsigned long addr); +#else +static inline bool is_cfi_trap(unsigned long addr) { return false; } #endif -#endif /* CONFIG_CFI_CLANG */ #ifdef CONFIG_MODULES #ifdef CONFIG_ARCH_USES_CFI_TRAPS