Re: x86: insn-eval.c's use of native_store_gdt()

[Thomas Gleixner <tglx@linutronix.de>]

On Fri, Feb 04 2022 at 10:23, Jan Beulich wrote:
> On 30.11.2021 12:09, Jan Beulich wrote:
>> I think it is b968e84b509d ("x86/iopl: Fake iopl(3) CLI/STI usage")
>> which uncovered an issue with get_desc() trying to access the GDT, as
>> introduced by 670f928ba09b ("x86/insn-eval: Add utility function to
>> get segment descriptor"). When running in a PV domain under Xen, the
>> (hypervisor's) GDT isn't accessible; with UMIP enabled by Xen even
>> SGDT wouldn't work, as the kernel runs in ring 3.
>> 
>> There's currently no hypercall to retrieve a descriptor from the GDT.
>> It is instead assumed that kernels know where their present GDT
>> lives. Can the native_store_gdt() be replaced there, please?
>> 
>> For context (I don't think it should matter much here) I'm observing
>> this with the kernel put underneath a rather old distro, where
>> hwclock triggers this path.
>
> I'd like to note that the issue still exists in 5.16.

I'd like to note, that I've seen no patches to that effect.

Thanks,

        tglx