Re: [PATCH 23/62] x86/idt: Move IDT to data segment

[Andy Lutomirski]

> On Feb 12, 2020, at 3:55 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote:
> 
> ïOn Tue, Feb 11, 2020 at 02:41:25PM -0800, Andy Lutomirski wrote:
>>> On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel <joro@xxxxxxxxxx> wrote:
>>> 
>>> From: Joerg Roedel <jroedel@xxxxxxx>
>>> 
>>> With SEV-ES, exception handling is needed very early, even before the
>>> kernel has cleared the bss segment. In order to prevent clearing the
>>> currently used IDT, move the IDT to the data segment.
>> 
>> Ugh.  At the very least this needs a comment in the code.
> 
> Yes, right, added a comment for that.
> 
>> I had a patch to fix the kernel ELF loader to clear BSS, which would
>> fix this problem once and for all, but it didn't work due to the messy
>> way that the decompressor handles memory.  I never got around to
>> fixing this, sadly.
> 
> Aren't there other ways of booting (Xen-PV?) which don't use the kernel
> ELF loader?

Dunno. I would hope the any sane loader would clear BSS before executing anything. This isnât currently the case, though. Oh well.

> 
> Regards,
> 
>    Joerg