Re: [tip:x86/asm] x86/umip: Add emulation code for UMIP instructions
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- Subject: Re: [tip:x86/asm] x86/umip: Add emulation code for UMIP instructions
- From: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
- Date: Wed, 8 Nov 2017 22:17:39 -0800
- Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Peter Anvin <hpa@xxxxxxxxx>, Borislav Petkov <bp@xxxxxxx>, Vlastimil Babka <vbabka@xxxxxxx>, Tony Luck <tony.luck@xxxxxxxxx>, Fenghua Yu <fenghua.yu@xxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, "Ravi V. Shankar" <ravi.v.shankar@xxxxxxxxx>, Chris Metcalf <cmetcalf@xxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>, Masami Hiramatsu <mhiramat@xxxxxxxxxx>, Andrew Lutomirski <luto@xxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, ray.huang@xxxxxxx, "Michael S. Tsirkin" <mst@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Chen Yucong <slaoub@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Jiri Slaby <jslaby@xxxxxxx>, Shuah Khan <shuah@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, "linux-tip-commits@xxxxxxxxxxxxxxx" <linux-tip-commits@xxxxxxxxxxxxxxx>
- In-reply-to: <dd612f93-1e21-ed53-4955-f753fbf0aa55@redhat.com>
- References: <1509935277-22138-8-git-send-email-ricardo.neri-calderon@linux.intel.com> <tip-1e5db223696afa55e6a038fac638f759e1fdcc01@git.kernel.org> <ca980b88-a668-29cc-3f5a-506088473282@redhat.com> <CA+55aFyzb5D6DfM_1mxcMbuYOaxZWFxqfv7WZS6zdkqnN7+p0A@mail.gmail.com> <3cdde8ac-500c-ddad-5ea5-a733e2c98d84@redhat.com> <CA+55aFzwOSbbGpV7dkmkOJ3ScP2pXqkkbPMjzU9qAmVyzSzoAw@mail.gmail.com> <68c11f7a-cd26-0fdc-0ac5-939a72c22227@redhat.com> <dd612f93-1e21-ed53-4955-f753fbf0aa55@redhat.com>
- User-agent: Mutt/1.5.24 (2015-08-30)
On Wed, Nov 08, 2017 at 06:14:12PM +0100, Paolo Bonzini wrote:
> On 08/11/2017 18:09, Denys Vlasenko wrote:
> > On 11/08/2017 05:57 PM, Linus Torvalds wrote:
> >> On Wed, Nov 8, 2017 at 8:53 AM, Denys Vlasenko <dvlasenk@xxxxxxxxxx>
> >> wrote:
> >>> We can postpone enabling UMIP by default by a year or so.
> >>> By this time, new Wine will be on majority of users' machines.
> >>
> >> So you are suggesting we run unnecessarily insecure, only in order to
> >> not do the emulation that we already have the code for and that the
> >> patch implements?
> >
> > We ran insecure in this way for ~25 years.
> >
> >> Why?
> >
> > To avoid having to maintain more obscure, rarely executed code.
>
> As a start, you could propose a patch to disable the emulation code
> through a sysctl or Kconfig symbol. I would be surprised if it takes
> more time than what you've spent writing emails in this thread.
Indeed, Andy Lutomirski suggested something similar in the past, but as a
separate series [1].
Plus, the Wine team was also interested in receiving the SIGSEGV that UMIP
would generate, but also acknowledged that it would break existing
versions[2].
Thanks and BR,
Ricardo
[1]. https://lkml.org/lkml/2017/3/8/735
[2]. https://www.winehq.org/pipermail/wine-devel/2016-November/115321.html
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