Re: [PATCH v3 00/17] x86: head_64.S spring cleaning

[Tom Lendacky]

On 11/22/22 15:42, Ard Biesheuvel wrote:
> On Tue, 22 Nov 2022 at 22:37, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> > On Tue, 22 Nov 2022 at 21:48, Tom Lendacky <thomas.lendacky@xxxxxxx> wrote:
> > > On 11/22/22 10:10, Ard Biesheuvel wrote:
> > > > After doing some cleanup work on the EFI code in head_64.S, the mixed
> > > > mode code in particular, I noticed that the memory encryption pieces
> > > > could use some attention as well, so I cleaned that up too.
> > > >
> > > > Changes since v2:
> > > > - add some clarifying comments to the EFI mixed mode changes
> > > > - include patch to make the EFI handover protocol optional that was sent
> > > >     out separately before
> > > > - rebase onto tip/master
> > > >
> > > > Changes since v1:
> > > > - at Boris's request, split the patches into smaller ones that are
> > > >     easier to review
> > > >
> > > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > > > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > > > Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> > > > Cc: Michael Roth <michael.roth@xxxxxxx>
> > >
> > > This causes an SEV guest to blow up on boot in the early boot code. It
> > > looks like the stack pointer is not valid and it triple faults on a pushq
> > > instruction (pushq $__KERNEL_CS in arch/x86/boot/compressed/head_64.S of
> > > startup_64).
> >
> > Thanks for the report.
> >
> > So the mystery here (at least to me) is that all the changes are to
> > the 32-bit code, and startup_64 reloads the stack pointer from the
> > symbol
> >
> > Does your config have CONFIG_EFI_MIXED enabled?
> >
> > Can I reproduce this fully emulated with QEMU? Or do I need a SEV host?
>
> Also, mind giving this a quick spin?

Just saw this after I sent out my email. Yes, this fixes it.

Thanks,
Tom

> diff --git a/drivers/firmware/efi/libstub/x86-stub.c
> b/drivers/firmware/efi/libstub/x86-stub.c
> index cb5f0befee57..1af11d34bc6c 100644
> --- a/drivers/firmware/efi/libstub/x86-stub.c
> +++ b/drivers/firmware/efi/libstub/x86-stub.c
> @@ -23,7 +23,7 @@
>
>   const efi_system_table_t *efi_system_table;
>   const efi_dxe_services_table_t *efi_dxe_table;
> -u32 image_offset;
> +u32 __section(".data") image_offset;
>   static efi_loaded_image_t *image = NULL;
>
>   static efi_status_t
>
> Thanks,
> Ard.