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

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Message-ID: <CAMj1kXHUQFAcRKzRkuGG3Rsyrexdi7_NUS1-aXrS36LP4Q=rxw@mail.gmail.com>
Date:   Tue, 22 Nov 2022 22:37:09 +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 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?

> Here is the Qemu register dump:
> RAX=00000000029cc260 RBX=ffffffffdd98c000 RCX=0000000000000010 RDX=0000000000000002
> RSI=000000003dec1000 RDI=0000000000000000 RBP=ffffffffdb000000 RSP=ffffffffde36e000
> R8 =000000003dec1410 R9 =000000003dec13fc R10=000000000000006c R11=0000000000000000
> R12=0000000000000000 R13=0000000000000001 R14=0000000000000004 R15=000000003eacdf44
> RIP=0000000002000263 RFL=00200002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> ES =0000 0000000000000000 00000000 00000000
> CS =0038 0000000000000000 ffffffff 00a09b00 DPL=0 CS64 [-RA]
> SS =0000 0000000000000000 00000000 00000000
> DS =0000 0000000000000000 00000000 00000000
> FS =0000 0000000000000000 00000000 00000000
> GS =0000 0000000000000000 00000000 00000000
> LDT=0000 0000000000000000 0000ffff 00008200 DPL=0 LDT
> TR =0000 0000000000000000 0000ffff 00008b00 DPL=0 TSS64-busy
> GDT=     00000000029cc270 0000002f
> IDT=     000000003f55e018 00000fff
> CR0=80010033 CR2=ffffffffde36dff8 CR3=000000003fc01000 CR4=00000668
> DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000
> DR6=00000000ffff0ff0 DR7=0000000000000400
> EFER=0000000000000d00
>
> Thanks,
> Tom
>
> >
> > Ard Biesheuvel (17):
> >    x86/compressed: efi-mixed: rename efi_thunk_64.S to efi-mixed.S
> >    x86/compressed: efi-mixed: move 32-bit entrypoint code into .text
> >      section
> >    x86/compressed: efi-mixed: move bootargs parsing out of 32-bit startup
> >      code
> >    x86/compressed: efi-mixed: move efi32_pe_entry into .text section
> >    x86/compressed: efi-mixed: move efi32_entry out of head_64.S
> >    x86/compressed: efi-mixed: move efi32_pe_entry() out of head_64.S
> >    x86/compressed: efi: merge multiple definitions of image_offset into
> >      one
> >    x86/compressed: efi-mixed: simplify IDT/GDT preserve/restore
> >    x86/compressed: avoid touching ECX in startup32_set_idt_entry()
> >    x86/compressed: pull global variable ref up into startup32_load_idt()
> >    x86/compressed: move startup32_load_idt() into .text section
> >    x86/compressed: move startup32_load_idt() out of head_64.S
> >    x86/compressed: move startup32_check_sev_cbit() into .text
> >    x86/compressed: move startup32_check_sev_cbit() out of head_64.S
> >    x86/compressed: adhere to calling convention in
> >      get_sev_encryption_bit()
> >    x86/compressed: only build mem_encrypt.S if AMD_MEM_ENCRYPT=y
> >    efi: x86: Make the deprecated EFI handover protocol optional
> >
> >   arch/x86/Kconfig                        |  17 +
> >   arch/x86/boot/compressed/Makefile       |   8 +-
> >   arch/x86/boot/compressed/efi_mixed.S    | 351 ++++++++++++++++++++
> >   arch/x86/boot/compressed/efi_thunk_64.S | 195 -----------
> >   arch/x86/boot/compressed/head_32.S      |   4 -
> >   arch/x86/boot/compressed/head_64.S      | 303 +----------------
> >   arch/x86/boot/compressed/mem_encrypt.S  | 152 ++++++++-
> >   arch/x86/boot/header.S                  |   2 +-
> >   arch/x86/boot/tools/build.c             |   2 +
> >   drivers/firmware/efi/libstub/x86-stub.c |   2 +-
> >   10 files changed, 533 insertions(+), 503 deletions(-)
> >   create mode 100644 arch/x86/boot/compressed/efi_mixed.S
> >   delete mode 100644 arch/x86/boot/compressed/efi_thunk_64.S
> >