x86/iopl: Fake iopl(3) CLI/STI usage

stable inclusion
from stable-5.10.81
commit b31bac061918936d6f6d647878bd45a2c81b446b
bugzilla: 185832 https://gitee.com/openeuler/kernel/issues/I4L9CF

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b31bac061918936d6f6d647878bd45a2c81b446b



--------------------------------

commit b968e84b upstream.

Since commit c8137ace ("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: a24ca997 ("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>
Cc: stable@kernel.org # v5.5+
Link: https://lkml.kernel.org/r/20210918090641.GD5106@worktop.programming.kicks-ass.net


Signed-off-by: Ondrej Zary <linux@zary.sk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>