From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id DA2696B5789 for ; Fri, 31 Aug 2018 11:02:10 -0400 (EDT) Received: by mail-oi0-f72.google.com with SMTP id q11-v6so11282027oih.15 for ; Fri, 31 Aug 2018 08:02:10 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id f186-v6sor7570431oig.110.2018.08.31.08.02.09 for (Google Transport Security); Fri, 31 Aug 2018 08:02:09 -0700 (PDT) MIME-Version: 1.0 References: <20180830143904.3168-1-yu-cheng.yu@intel.com> <20180830143904.3168-7-yu-cheng.yu@intel.com> In-Reply-To: <20180830143904.3168-7-yu-cheng.yu@intel.com> From: Jann Horn Date: Fri, 31 Aug 2018 17:01:42 +0200 Message-ID: Subject: Re: [RFC PATCH v3 06/24] x86/cet: Control protection exception handler Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: yu-cheng.yu@intel.com Cc: the arch/x86 maintainers , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , hjl.tools@gmail.com, Jonathan Corbet , keescook@chromiun.org, Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , ravi.v.shankar@intel.com, vedvyas.shanbhogue@intel.com On Thu, Aug 30, 2018 at 4:43 PM Yu-cheng Yu wrote: > > A control protection exception is triggered when a control flow transfer > attempt violated shadow stack or indirect branch tracking constraints. > For example, the return address for a RET instruction differs from the > safe copy on the shadow stack; or a JMP instruction arrives at a non- > ENDBR instruction. > > The control protection exception handler works in a similar way as the > general protection fault handler. Is there a reason why all the code in this patch isn't #ifdef'ed away on builds that don't support CET? It looks like the CET handler is hooked up to the IDT conditionally, but the handler code is always built? > Signed-off-by: Yu-cheng Yu > --- > arch/x86/entry/entry_64.S | 2 +- > arch/x86/include/asm/traps.h | 3 ++ > arch/x86/kernel/idt.c | 4 +++ > arch/x86/kernel/traps.c | 58 ++++++++++++++++++++++++++++++++++++ > 4 files changed, 66 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > index 957dfb693ecc..5f4914e988df 100644 > --- a/arch/x86/entry/entry_64.S > +++ b/arch/x86/entry/entry_64.S > @@ -1000,7 +1000,7 @@ idtentry spurious_interrupt_bug do_spurious_interrupt_bug has_error_code=0 > idtentry coprocessor_error do_coprocessor_error has_error_code=0 > idtentry alignment_check do_alignment_check has_error_code=1 > idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0 > - > +idtentry control_protection do_control_protection has_error_code=1 > > /* > * Reload gs selector with exception handling > diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h > index 3de69330e6c5..5196050ff3d5 100644 > --- a/arch/x86/include/asm/traps.h > +++ b/arch/x86/include/asm/traps.h > @@ -26,6 +26,7 @@ asmlinkage void invalid_TSS(void); > asmlinkage void segment_not_present(void); > asmlinkage void stack_segment(void); > asmlinkage void general_protection(void); > +asmlinkage void control_protection(void); > asmlinkage void page_fault(void); > asmlinkage void async_page_fault(void); > asmlinkage void spurious_interrupt_bug(void); > @@ -77,6 +78,7 @@ dotraplinkage void do_stack_segment(struct pt_regs *, long); > dotraplinkage void do_double_fault(struct pt_regs *, long); > #endif > dotraplinkage void do_general_protection(struct pt_regs *, long); > +dotraplinkage void do_control_protection(struct pt_regs *, long); > dotraplinkage void do_page_fault(struct pt_regs *, unsigned long); > dotraplinkage void do_spurious_interrupt_bug(struct pt_regs *, long); > dotraplinkage void do_coprocessor_error(struct pt_regs *, long); > @@ -142,6 +144,7 @@ enum { > X86_TRAP_AC, /* 17, Alignment Check */ > X86_TRAP_MC, /* 18, Machine Check */ > X86_TRAP_XF, /* 19, SIMD Floating-Point Exception */ > + X86_TRAP_CP = 21, /* 21 Control Protection Fault */ > X86_TRAP_IRET = 32, /* 32, IRET Exception */ > }; > > diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c > index 01adea278a71..2d02fdd599a2 100644 > --- a/arch/x86/kernel/idt.c > +++ b/arch/x86/kernel/idt.c > @@ -104,6 +104,10 @@ static const __initconst struct idt_data def_idts[] = { > #elif defined(CONFIG_X86_32) > SYSG(IA32_SYSCALL_VECTOR, entry_INT80_32), > #endif > + > +#ifdef CONFIG_X86_INTEL_CET > + INTG(X86_TRAP_CP, control_protection), > +#endif > }; > > /* > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index e6db475164ed..21a713b96148 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -578,6 +578,64 @@ do_general_protection(struct pt_regs *regs, long error_code) > } > NOKPROBE_SYMBOL(do_general_protection); > > +static const char *control_protection_err[] = > +{ > + "unknown", > + "near-ret", > + "far-ret/iret", > + "endbranch", > + "rstorssp", > + "setssbsy", > +}; > + > +/* > + * When a control protection exception occurs, send a signal > + * to the responsible application. Currently, control > + * protection is only enabled for the user mode. This > + * exception should not come from the kernel mode. > + */ > +dotraplinkage void > +do_control_protection(struct pt_regs *regs, long error_code) > +{ > + struct task_struct *tsk; > + > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + if (notify_die(DIE_TRAP, "control protection fault", regs, > + error_code, X86_TRAP_CP, SIGSEGV) == NOTIFY_STOP) > + return; > + cond_local_irq_enable(regs); > + > + if (!user_mode(regs)) > + die("kernel control protection fault", regs, error_code); > + > + if (!static_cpu_has(X86_FEATURE_SHSTK) && > + !static_cpu_has(X86_FEATURE_IBT)) > + WARN_ONCE(1, "CET is disabled but got control " > + "protection fault\n"); > + > + tsk = current; > + tsk->thread.error_code = error_code; > + tsk->thread.trap_nr = X86_TRAP_CP; > + > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) && > + printk_ratelimit()) { > + unsigned int max_err; > + > + max_err = ARRAY_SIZE(control_protection_err) - 1; > + if ((error_code < 0) || (error_code > max_err)) > + error_code = 0; > + pr_info("%s[%d] control protection ip:%lx sp:%lx error:%lx(%s)", > + tsk->comm, task_pid_nr(tsk), > + regs->ip, regs->sp, error_code, > + control_protection_err[error_code]); > + print_vma_addr(" in ", regs->ip); Shouldn't this be using KERN_CONT, like other callers of print_vma_addr(), to get the desired output? > + pr_cont("\n"); > + } > + > + force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk);