linux-kernel - Re: [PATCH v3 00/17] x86: head

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Date:   Tue, 22 Nov 2022 22:42:50 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michael Roth <michael.roth@....com>
Subject: Re: [PATCH v3 00/17] x86: head_64.S spring cleaning

On Tue, 22 Nov 2022 at 22:37, Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Tue, 22 Nov 2022 at 21:48, Tom Lendacky <thomas.lendacky@....com> 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@...utronix.de>
> > > Cc: Ingo Molnar <mingo@...hat.com>
> > > Cc: Borislav Petkov <bp@...en8.de>
> > > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > > Cc: Michael Roth <michael.roth@....com>
> >
> > 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?

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.