linux-kernel - Re: [RFC][PATCH] x86,ibt: Use UDB instead of 0xEA

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Message-ID: <20250814112328.GC4068168@noisy.programming.kicks-ass.net>
Date: Thu, 14 Aug 2025 13:23:28 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc: kees@...nel.org, alyssa.milburn@...el.com, scott.d.constable@...el.com,
	joao@...rdrivepizza.com, andrew.cooper3@...rix.com,
	samitolvanen@...gle.com, nathan@...nel.org,
	alexei.starovoitov@...il.com, mhiramat@...nel.org, ojeda@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] x86,ibt: Use UDB instead of 0xEA

On Thu, Aug 14, 2025 at 01:17:33PM +0200, Peter Zijlstra wrote:
> diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
> index 99444409c026..59f8bf022ec5 100644
> --- a/arch/x86/kernel/cet.c
> +++ b/arch/x86/kernel/cet.c
> @@ -123,7 +123,7 @@ static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code)
>  		return;
>  	}
>  
> -	pr_err("Missing ENDBR: %pS\n", (void *)instruction_pointer(regs));
> +	early_printk("Missing ENDBR: %pS\n", (void *)instruction_pointer(regs));
>  	if (!ibt_fatal) {
>  		printk(KERN_DEFAULT CUT_HERE);
>  		__warn(__FILE__, __LINE__, (void *)regs->ip, TAINT_WARN, regs, NULL);

Obviously this is debugging remnant and will go away.