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From: hpa@zytor.com
To: Thomas Gleixner <tglx@linutronix.de>, Willy Tarreau <w@1wt.eu>
Cc: 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>
Subject: Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further
Date: Thu, 07 Nov 2019 02:19:19 -0800	[thread overview]
Message-ID: <71DE81AC-3AD4-47B3-9CBA-A2C7841A3370@zytor.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1911071058260.4256@nanos.tec.linutronix.de>

On November 7, 2019 2:00:27 AM PST, Thomas Gleixner <tglx@linutronix.de> wrote:
>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

This seems very undesirable... 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.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

  parent reply	other threads:[~2019-11-07 10:21 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-06 19:34 [patch 0/9] x86/iopl: Prevent user space from using CLI/STI with iopl(3) Thomas Gleixner
2019-11-06 19:35 ` [patch 1/9] x86/ptrace: Prevent truncation of bitmap size Thomas Gleixner
2019-11-07  7:31   ` Ingo Molnar
2019-11-06 19:35 ` [patch 2/9] x86/process: Unify copy_thread_tls() Thomas Gleixner
2019-11-08 22:31   ` Andy Lutomirski
2019-11-08 23:43     ` Thomas Gleixner
2019-11-10 12:36       ` Thomas Gleixner
2019-11-10 16:56         ` Andy Lutomirski
2019-11-11  8:52           ` Peter Zijlstra
2019-11-06 19:35 ` [patch 3/9] x86/cpu: Unify cpu_init() Thomas Gleixner
2019-11-08 22:34   ` Andy Lutomirski
2019-11-06 19:35 ` [patch 4/9] x86/io: Speedup schedule out of I/O bitmap user Thomas Gleixner
2019-11-07  9:12   ` Peter Zijlstra
2019-11-07 14:04     ` Thomas Gleixner
2019-11-07 14:08       ` Thomas Gleixner
2019-11-08 22:41         ` Andy Lutomirski
2019-11-08 23:45           ` Thomas Gleixner
2019-11-09  3:32             ` Andy Lutomirski
2019-11-10 12:43               ` Thomas Gleixner
2019-11-09  0:24   ` Andy Lutomirski
2019-11-06 19:35 ` [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further Thomas Gleixner
2019-11-07  1:11   ` Linus Torvalds
2019-11-07  7:44     ` Thomas Gleixner
2019-11-07  8:25     ` Ingo Molnar
2019-11-07  9:17       ` Willy Tarreau
2019-11-07 10:00         ` Thomas Gleixner
2019-11-07 10:13           ` Willy Tarreau
2019-11-07 10:19           ` hpa [this message]
2019-11-07 10:27             ` Willy Tarreau
2019-11-07 10:50               ` hpa
2019-11-07 12:56                 ` Willy Tarreau
2019-11-07 16:45                   ` Eric W. Biederman
2019-11-07 16:53                     ` Linus Torvalds
2019-11-07 16:57                     ` Willy Tarreau
2019-11-10 17:17       ` Andy Lutomirski
2019-11-07  7:37   ` Ingo Molnar
2019-11-07  7:45     ` Thomas Gleixner
2019-11-07  8:16   ` Ingo Molnar
2019-11-07 18:02     ` Thomas Gleixner
2019-11-07 19:24   ` Brian Gerst
2019-11-07 19:54     ` Linus Torvalds
2019-11-07 21:00       ` Brian Gerst
2019-11-07 21:32         ` Thomas Gleixner
2019-11-07 23:20           ` hpa
2019-11-07 21:44         ` Linus Torvalds
2019-11-08  1:12           ` H. Peter Anvin
2019-11-08  2:12             ` Brian Gerst
2019-11-10 17:21           ` Andy Lutomirski
2019-11-06 19:35 ` [patch 6/9] x86/iopl: Fixup misleading comment Thomas Gleixner
2019-11-06 19:35 ` [patch 7/9] x86/iopl: Restrict iopl() permission scope Thomas Gleixner
2019-11-07  9:09   ` Peter Zijlstra
2019-11-10 17:26   ` Andy Lutomirski
2019-11-10 20:31     ` Thomas Gleixner
2019-11-10 21:05       ` Andy Lutomirski
2019-11-10 21:21         ` Thomas Gleixner
2019-11-06 19:35 ` [patch 8/9] x86/iopl: Remove legacy IOPL option Thomas Gleixner
2019-11-07  6:11   ` Jürgen Groß
2019-11-07  6:26     ` hpa
2019-11-07 16:44     ` Stephen Hemminger
2019-11-07  9:13   ` Peter Zijlstra
2019-11-06 19:35 ` [patch 9/9] selftests/x86/iopl: Verify that CLI/STI result in #GP Thomas Gleixner
2019-11-07  7:28 ` [patch] x86/iopl: Remove unused local variable, update comments in ksys_ioperm() Ingo Molnar

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