linux-kernel - Re: [PATCH v2 07/39] x86/cet: Add user control-protection fault handler

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Date:   Mon, 3 Oct 2022 17:01:09 +0300
From:   "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH v2 07/39] x86/cet: Add user control-protection fault
 handler

On Thu, Sep 29, 2022 at 03:29:04PM -0700, Rick Edgecombe wrote:
> +#else
> +static void do_user_control_protection_fault(struct pt_regs *regs,
> +					     unsigned long error_code)
> +{
> +	WARN_ONCE(1, "User-mode control protection fault with shadow support disabled\n");

Why is this a warning, but runtime check for !X86_FEATURE_IBT and
!X86_FEATURE_SHSTK below is fatal?

> +}
> +#endif
> +
> +#ifdef CONFIG_X86_KERNEL_IBT
> +
> +static __ro_after_init bool ibt_fatal = true;
> +
> +extern void ibt_selftest_ip(void); /* code label defined in asm below */
>  
> +static void do_kernel_control_protection_fault(struct pt_regs *regs)
> +{
>  	if (unlikely(regs->ip == (unsigned long)&ibt_selftest_ip)) {
>  		regs->ax = 0;
>  		return;
> @@ -283,9 +335,29 @@ static int __init ibt_setup(char *str)
>  }
>  
>  __setup("ibt=", ibt_setup);
> -
> +#else
> +static void do_kernel_control_protection_fault(struct pt_regs *regs)
> +{
> +	WARN_ONCE(1, "Kernel-mode control protection fault with IBT disabled\n");

Ditto.

> +}
>  #endif /* CONFIG_X86_KERNEL_IBT */
>  
> +#if defined(CONFIG_X86_KERNEL_IBT) || defined(CONFIG_X86_SHADOW_STACK)
> +DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
> +{
> +	if (!cpu_feature_enabled(X86_FEATURE_IBT) &&
> +	    !cpu_feature_enabled(X86_FEATURE_SHSTK)) {
> +		pr_err("Unexpected #CP\n");
> +		BUG();
> +	}
> +
> +	if (user_mode(regs))
> +		do_user_control_protection_fault(regs, error_code);
> +	else
> +		do_kernel_control_protection_fault(regs);
> +}
> +#endif /* defined(CONFIG_X86_KERNEL_IBT) || defined(CONFIG_X86_SHADOW_STACK) */
> +
>  #ifdef CONFIG_X86_F00F_BUG
>  void handle_invalid_op(struct pt_regs *regs)
>  #else

-- 
  Kiryl Shutsemau / Kirill A. Shutemov