From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eugene Syromiatnikov Subject: Re: [RFC PATCH v4 06/27] x86/cet: Control protection exception handler Date: Wed, 3 Oct 2018 12:39:59 +0200 Message-ID: <20181003103959.GB7111@asgard.redhat.com> References: <20180921150351.20898-1-yu-cheng.yu@intel.com> <20180921150351.20898-7-yu-cheng.yu@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180921150351.20898-7-yu-cheng.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Yu-cheng Yu Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek Peter List-Id: linux-arch.vger.kernel.org On Fri, Sep 21, 2018 at 08:03:30AM -0700, Yu-cheng Yu wrote: > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index e6db475164ed..873765adc244 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(KERN_CONT " in ", regs->ip); > + pr_cont("\n"); > + } > + > + force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk); That way, no information is provided to userspace (both application and debugger), which is rather unfortunate. It would be nice if a new SEGV_* code was added at least, and CET error (with error code constant provided in UAPI) is passed via si_errno. (Having ip/sp/*ssp would be even better, but I'm not exactly sure about ramifications of providing this kind of information to user space). From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:50032 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726517AbeJCR13 (ORCPT ); Wed, 3 Oct 2018 13:27:29 -0400 Date: Wed, 3 Oct 2018 12:39:59 +0200 From: Eugene Syromiatnikov Subject: Re: [RFC PATCH v4 06/27] x86/cet: Control protection exception handler Message-ID: <20181003103959.GB7111@asgard.redhat.com> References: <20180921150351.20898-1-yu-cheng.yu@intel.com> <20180921150351.20898-7-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180921150351.20898-7-yu-cheng.yu@intel.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Yu-cheng Yu Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue Message-ID: <20181003103959.jk-C_lCqrfEqjK46StL1HUA6tGYD2uWiYa00JM9X0N0@z> On Fri, Sep 21, 2018 at 08:03:30AM -0700, Yu-cheng Yu wrote: > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index e6db475164ed..873765adc244 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(KERN_CONT " in ", regs->ip); > + pr_cont("\n"); > + } > + > + force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk); That way, no information is provided to userspace (both application and debugger), which is rather unfortunate. It would be nice if a new SEGV_* code was added at least, and CET error (with error code constant provided in UAPI) is passed via si_errno. (Having ip/sp/*ssp would be even better, but I'm not exactly sure about ramifications of providing this kind of information to user space).