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

[JÃrgen GroÃ]

On 12.02.20 17:23, Andy Lutomirski wrote:
> > 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.

Xen-PV is clearing BSS as the very first action.


Juergen