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    SubjectRe: [PATCH] x86/iopl: Fake iopl(3) CLI/STI usage
    Date
    On Fri, Sep 17 2021 at 11:20, Peter Zijlstra wrote:
    > Subject: x86/iopl: Fake iopl(3) CLI/STI usage
    > From: Peter Zijlstra <peterz@infradead.org>
    > Date: Thu, 16 Sep 2021 23:05:09 +0200
    >
    > Since commit c8137ace5638 ("x86/iopl: Restrict iopl() permission
    > scope") it's possible to emulate iopl(3) using ioperm(), except for
    > the CLI/STI usage.
    >
    > Userspace CLI/STI usage is very dubious (read broken), since any
    > exception taken during that window can lead to rescheduling anyway (or
    > worse). The IOPL(2) manpage even states that usage of CLI/STI is highly
    > discouraged and might even crash the system.
    >
    > Of course, that won't stop people and HP has the dubious honour of
    > being the first vendor to be found using this in their hp-health
    > package.
    >
    > In order to enable this 'software' to still 'work', have the #GP treat
    > the CLI/STI instructions as NOPs when iopl(3). Warn the user that
    > their program is doing dubious things.
    >
    > Fixes: a24ca9976843 ("x86/iopl: Remove legacy IOPL option")
    > Reported-by: Ondrej Zary <linux@zary.sk>
    > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

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