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Date:   Mon, 3 Oct 2022 17:01:09 +0300
From:   "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
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        Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [PATCH v2 07/39] x86/cet: Add user control-protection fault
 handler
Message-ID: <20221003140109.jgn3per7vbthifn5@box.shutemov.name>
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
 <20220929222936.14584-8-rick.p.edgecombe@intel.com>
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In-Reply-To: <20220929222936.14584-8-rick.p.edgecombe@intel.com>
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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