linux-kernel - Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further

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Date:   Thu, 7 Nov 2019 11:00:27 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Willy Tarreau <w@....eu>
cc:     Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Juergen Gross <jgross@...e.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage
 further

On Thu, 7 Nov 2019, Willy Tarreau wrote:
> On Thu, Nov 07, 2019 at 09:25:41AM +0100, Ingo Molnar wrote:
> > I.e. the model I'm suggesting is that if a task uses ioperm() or iopl() 
> > then it should have a bitmap from that point on until exit(), even if 
> > it's all zeroes or all ones. Most applications that are using those 
> > primitives really need it all the time and are using just a few ioports, 
> > so all the tracking doesn't help much anyway.
> 
> I'd go even further, considering that any task having called ioperm()
> or iopl() once is granted access to all 64k ports for life: if the task
> was granted access to any port, it will be able to request access for any
> other port anyway. And we cannot claim that finely filtering accesses
> brings any particular reliability in my opinion, considering that it's
> generally possible to make the system really sick by starting to play
> with most I/O ports. So for me that becomes a matter of trusted vs not
> trusted task. Then we can simply have two pages of 0xFF to describe
> their I/O access bitmap.
> 
> > On a related note, another simplification would be that in principle we 
> > could also use just a single bitmap and emulate iopl() as an ioperm(all) 
> > or ioperm(none) calls. Yeah, it's not fully ABI compatible for mixed 
> > ioperm()/iopl() uses, but is that ABI actually being relied on in 
> > practice?
> 
> You mean you'd have a unified map for all tasks ? In this case I think
> it's simpler and equivalent to simply ignore the values in the calls
> and grant full perms to the 64k ports range after the calls were
> validated. I could be totally wrong and missing something obvious
> though.

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.

Thanks,

	tglx