linux-kernel - Re: [PATCH v13 00/16] Enable FSGSBASE instructions

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Date:   Thu, 18 Jun 2020 20:25:30 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Sasha Levin <sashal@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Tony Luck <tony.luck@...el.com>,
        "Bae\, Chang Seok" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "open list\:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Subject: Re: [PATCH v13 00/16] Enable FSGSBASE instructions

Andy Lutomirski <luto@...nel.org> writes:
> Is there a plan to deal with:
>
>         /*
>          * This function has some ABI oddities.
>          *
>          * A 32-bit ptracer probably expects that writing FS or GS will change
>          * FSBASE or GSBASE respectively.  In the absence of FSGSBASE support,
>          * this code indeed has that effect.  When FSGSBASE is added, this
>          * will require a special case.
>          *
>          * For existing 64-bit ptracers, writing FS or GS *also* currently
>          * changes the base if the selector is nonzero the next time the task
>          * is run.  This behavior may? not be needed, and trying to preserve it
>          * when FSGSBASE is added would be complicated at best.
>          */
>
> in arch/x86/kernel/ptrace.c?

Not that I'm aware of.