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

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Message-ID: <51c25fb7-46be-4364-9371-6a7cb6b07625@orca.pet>
Date: Mon, 1 Sep 2025 13:43:15 +0200
From: Marcos Del Sol Vives <marcos@...a.pet>
To: "H. Peter Anvin" <hpa@...or.com>,
 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

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.