Messages in this thread | | | Date | Thu, 7 Nov 2019 11:00:27 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further |
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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
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