linux-kernel - Re: [patch V2 14/16] x86/iopl: Restrict iopl() permission scope

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Date:   Tue, 12 Nov 2019 10:35:39 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Willy Tarreau <w@....eu>, Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch V2 14/16] x86/iopl: Restrict iopl() permission scope

On Mon, Nov 11, 2019 at 2:35 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> From: Thomas Gleixner <tglx@...utronix.de>
>
> The access to the full I/O port range can be also provided by the TSS I/O
> bitmap, but that would require to copy 8k of data on scheduling in the
> task. As shown with the sched out optimization TSS.io_bitmap_base can be
> used to switch the incoming task to a preallocated I/O bitmap which has all
> bits zero, i.e. allows access to all I/O ports.
>
> Implementing this allows to provide an iopl() emulation mode which restricts
> the IOPL level 3 permissions to I/O port access but removes the STI/CLI
> permission which is coming with the hardware IOPL mechansim.
>
> Provide a config option to switch IOPL to emulation mode, make it the
> default and while at it also provide an option to disable IOPL completely.

Acked-by: Andy Lutomirski <luto@...nel.org>