linux-kernel - Re: [PATCH v2] x86,ibt: Use UDB instead of 0xEA

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Message-ID: <7623dfcf-f6ed-4caf-bb60-7fa953f0778c@zytor.com>
Date: Tue, 28 Oct 2025 11:55:57 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc: X86 ML <x86@...nel.org>, Kees Cook <kees@...nel.org>,
        alyssa.milburn@...el.com, scott.d.constable@...el.com,
        Joao Moreira <joao@...rdrivepizza.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Masami Hiramatsu
 <mhiramat@...nel.org>, ojeda@...nel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] x86,ibt: Use UDB instead of 0xEA

On 2025-09-02 12:37, Alexei Starovoitov wrote:
> 
> I suspect that 'reserved' opcode will not be used any time soon.
> If 10 years from now the opcode is used in some future CPU that CPU
> is better to be not vulnerable and CFI, FineIBT things will be
> gone from the kernel by then.
> So I would do absolutely nothing and just ignore the lack of blessing.
> 

What makes you say that? *Please* don't make these kinds of assumptions -- it
causes massive headaches for both us chip makers and for users.

	-hpa