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Re: x86: insn-eval.c's use of native_store_gdt()
- To: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 4 Feb 2022 10:23:54 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>
- Delivery-date: Fri, 04 Feb 2022 09:24:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Jan
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