Re: [PATCH] kfence: add kfence.fault parameter

[Alexander Potapenko <glider@google.com>]

> @@ -830,7 +835,8 @@ static void kfence_check_all_canary(void)
>  static int kfence_check_canary_callback(struct notifier_block *nb,
>                                         unsigned long reason, void *arg)
>  {
> -       kfence_check_all_canary();
> +       if (READ_ONCE(kfence_enabled))
> +               kfence_check_all_canary();

By the way, should we also check for kfence_enabled when reporting errors?


> @@ -1307,12 +1314,14 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
>         if (to_report) {
>                 raw_spin_lock_irqsave(&to_report->lock, flags);
>                 to_report->unprotected_page = unprotected_page;
> -               kfence_report_error(addr, is_write, regs, to_report, error_type);
> +               fault = kfence_report_error(addr, is_write, regs, to_report, error_type);
>                 raw_spin_unlock_irqrestore(&to_report->lock, flags);
>         } else {
>                 /* This may be a UAF or OOB access, but we can't be sure. */
> -               kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID);
> +               fault = kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID);
>         }
>
> +       kfence_handle_fault(fault);
> +
>         return kfence_unprotect(addr); /* Unprotect and let access proceed. */

If kfence_handle_fault() oopses, kfence_unprotect() will never be
called, is that the desired behavior?


>         /* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */
>         if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
> -               return;
> +               return KFENCE_FAULT_NONE;

We explicitly don't panic here; guess it should be fine...