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Date:   Thu, 07 Nov 2019 02:50:20 -0800
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Subject: Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further
To:     Willy Tarreau <w@1wt.eu>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Stephen Hemminger <stephen@networkplumber.org>,
        Juergen Gross <jgross@suse.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
From:   hpa@zytor.com
Message-ID: <5AAEF116-EC9D-4C58-878F-9D27189E123A@zytor.com>
Sender: linux-kernel-owner@vger.kernel.org
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On November 7, 2019 2:27:56 AM PST, Willy Tarreau <w@1wt=2Eeu> wrote:
>On Thu, Nov 07, 2019 at 02:19:19AM -0800, hpa@zytor=2Ecom wrote:
>> >Changing ioperm(single port, port range) to be ioperm(all) is going
>to
>> >break a bunch of test cases which actually check whether the
>permission
>> >is restricted to a single I/O port or the requested port range=2E
>> >
>> >Thanks,
>> >
>> >	tglx
>>=20
>> This seems very undesirable=2E=2E=2E as much as we might wish otherwise=
,
>the port
>> bitmap is the equivalent to the MMU, and there are definitely users
>doing
>> direct device I/O out there=2E
>
>Doing these, sure, but doing these while ranges are really checked ?
>I mean, the MMU grants you access to the pages you were assigned=2E Here
>with the I/O bitmap you just have to ask for access to port X and you
>get it=2E I could understand the benefit if we had EBUSY in return but
>that's not the case, you can actually request access to a port range
>another device driver or process is currently using, and mess up with
>what it does even by accident=2E I remember streaming 1-bit music in
>userland from the LED of my floppy drive in the late-90s, it used to
>cause some trouble to the floppy driver when using mtools in parallel
>:-)
>
>Willy

You get access to the ports you are assigned, just like pages you are assi=
gned=2E=2E=2E the rest is kernel policy, or, for that matter, privileged us=
erspace (get permissions to the necessary ports, then drop privilege=2E=2E=
=2E the usual stuff=2E)

--=20
Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E