Re: [PATCH] v5.10 backport of x86/iopl: Fake iopl(3) CLI/STI usage

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Nov 16, 2021 at 08:15:14PM +0100, Ondrej Zary wrote:
> Backport of the following patch for 5.10-stable:
> 
> >>>From b968e84b509da593c50dc3db679e1d33de701f78 Mon Sep 17 00:00:00 2001
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Fri, 17 Sep 2021 11:20:04 +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>
> Link: https://lkml.kernel.org/r/20210918090641.GD5106@worktop.programming.kicks-ass.net
> Signed-off-by: Ondrej Zary <linux@zary.sk>

Now queued up, thanks.

greg k-h