On Fri, Feb 05, 2021 at 10:00:21AM -0800, Yu, Yu-cheng wrote: > On 2/5/2021 5:59 AM, Borislav Petkov wrote: > > On Wed, Feb 03, 2021 at 02:55:28PM -0800, Yu-cheng Yu wrote: > > > +DEFINE_IDTENTRY_ERRORCODE(exc_control_protection) > > > +{ > > > + static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL, > > > + DEFAULT_RATELIMIT_BURST); > > > + struct task_struct *tsk; > > > + > > > + if (!user_mode(regs)) { > > > + pr_emerg("PANIC: unexpected kernel control protection fault\n"); > > > + die("kernel control protection fault", regs, error_code); > > > + panic("Machine halted."); > > > + } > > > + > > > + cond_local_irq_enable(regs); > > > + > > > + if (!boot_cpu_has(X86_FEATURE_CET)) > > > + WARN_ONCE(1, "Control protection fault with CET support > > > disabled\n"); > > > + > > > + tsk = current; > > > + tsk->thread.error_code = error_code; > > > + tsk->thread.trap_nr = X86_TRAP_CP; > > > + > > > + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) && > > > + __ratelimit(&rs)) { > > > > I can't find it written down anywhere why the ratelimiting is needed at > > all? > > > > The ratelimit here is only for #CP, and its rate is not counted together > with other types of faults. If a task gets here, it will exit. The only > condition the ratelimit will trigger is when multiple tasks hit #CP at once, > which is unlikely. Are you suggesting that we do not need the ratelimit > here?
Since this is a potentially unprivileged-userspace-triggerable condition, I tend to prefer having a ratelimit. I don't feel _strongly_ about it, but I find it better to be defensive against log spamming (whether malicious or accidental). -- Kees Cook