From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga02.intel.com ([134.134.136.20]:9897 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726950AbeJCXKu (ORCPT ); Wed, 3 Oct 2018 19:10:50 -0400 Message-ID: <9c93e864e5996862cb5fdb66d4140faa634cbc47.camel@intel.com> Subject: Re: [RFC PATCH v4 06/27] x86/cet: Control protection exception handler From: Yu-cheng Yu Date: Wed, 03 Oct 2018 09:11:34 -0700 In-Reply-To: <20181003103959.GB7111@asgard.redhat.com> References: <20180921150351.20898-1-yu-cheng.yu@intel.com> <20180921150351.20898-7-yu-cheng.yu@intel.com> <20181003103959.GB7111@asgard.redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Eugene Syromiatnikov 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: <20181003161134.bHI-DnOERn9bKzysPQLtsF7D8jroMCYUghf7bfy6WF0@z> On Wed, 2018-10-03 at 12:39 +0200, Eugene Syromiatnikov wrote: > On Fri, Sep 21, 2018 at 08:03:30AM -0700, Yu-cheng Yu wrote: > > +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). Ok, I will add that. Yu-cheng