linux-kernel - Re: [PATCH v2] x86: add hintable NOPs emulation

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Message-ID: <772C4DE8-8564-430D-9304-A39F88E07EBF@zytor.com>
Date: Mon, 01 Sep 2025 14:28:04 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Marcos Del Sol Vives <marcos@...a.pet>,
        kernel test robot <oliver.sang@...el.com>
CC: oe-lkp@...ts.linux.dev, lkp@...el.com, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, Kees Cook <kees@...nel.org>,
        "Xin Li (Intel)" <xin@...or.com>,
        Sabyrzhan Tasbolatov <snovitoll@...il.com>
Subject: Re: [PATCH v2] x86: add hintable NOPs emulation

On September 1, 2025 4:43:15 AM PDT, Marcos Del Sol Vives <marcos@...a.pet> wrote:
>El 31/08/2025 a las 21:32, H. Peter Anvin escribió:
>> I'm really, *really* starting to question this approach. 
>> 
>> The right thing would be to not compile in endbr instructions on 32 bits,
>> since they aren't supported by the kernel (if you try to enable CET/IBT
>> you will crash instantly, because there is no endbr32 at the vdso system
>> can entry point right now.)
>> 
>> We are talking about a very small number of CPUs stuck between generation
>> 5 and generation 6. Most likely we are talking about a much smaller number
>> than the i486 support we have been debating lately...
>
>I assume the kernel is currently simply ignoring the CET flag on ELF for
>all 32-bit x86 binaries and libraries?
>
>Anyhow, seeing this is indeed becoming more tricky and error-prone, I'm
>contating the sudo developer which is, so far, the only software that
>has this issue.

Yep.