linux-kernel - Re: [PATCH 3/3] x86: Disable running 32bit processes if ia32

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Message-ID: <87v8fyhrrw.ffs@tglx>
Date:   Thu, 08 Jun 2023 17:56:19 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Nikolay Borisov <nik.borisov@...e.com>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, mhocko@...e.com, jslaby@...e.cz
Subject: Re: [PATCH 3/3] x86: Disable running 32bit processes if
 ia32_disabled is passed

On Thu, Jun 08 2023 at 12:25, Andrew Cooper wrote:
> On 08/06/2023 1:25 am, Thomas Gleixner wrote:
>> I really wish that we could disable syscall32 reliably on AMD and make
>> it raise #UD as it does on Intal.
>
> You know that's changing in FRED, and will follow the AMD model?
>
> The SYSCALL instruction is lower latency if it doesn't need to check %cs
> to conditionally #UD.

Yes, but with FRED the CPL0 context is fully consistent. There are no
CPL3 leftovers.

>> Didn't we assume that there are no CPU bugs? :)
>
> Tell me, is such a CPU delivered with or without a complimentary unicorn? :)

It's deliverd by a fairytale princess :)

Thanks,

        tglx