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Message-Id: <01288fc6-4525-48a5-8ab5-0c617fdbcfc9@www.fastmail.com>
Date:   Tue, 21 Sep 2021 14:01:40 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:     "Ondrej Zary" <linux@...y.sk>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/iopl: Fake iopl(3) CLI/STI usage


On Sat, Sep 18, 2021, at 12:05 AM, Peter Zijlstra wrote:
> On Fri, Sep 17, 2021 at 03:24:51PM -0700, Linus Torvalds wrote:
>> On Fri, Sep 17, 2021 at 3:23 PM Linus Torvalds
>> <torvalds@...ux-foundation.org> wrote:
>> >
>> > I think the proper thing to do is perhaps something like
>> 
>> The alternative is to just ignore cs_abse entirely, and just use
>> "regs->ip", which makes this all even easier.
>> 
>> If somebody uses a code segment _and_ cli/sti, maybe they should just
>> get the SIGSEGV?
>
> I did a hatched job on fixup_ump_exception() which is why it looks like
> it does, that said...
>
> our case at hand mmap()'s BIOS code from /dev/mem and executes that, I
> don't think it does an LDT segment but it would be entirely in line with
> the level of hack we're looking at.
>
> Let me frob at this after breakfast and see if I can make it better.

The patch seems fine, but I have to ask: is this really worth fixing?

I suppose the log message could check if the computer comes from HP(E) and gently that the owner switch vendors.

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