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

[Tom Lendacky]

On 11/22/22 15:37, Ard Biesheuvel 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

I bisected it to:

99b7f4b23d9f ("x86/boot/compressed, efi: Merge multiple definitions of image_offset into one")

And doing the following fixed it:

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index cb5f0befee57..a0bfd31358ba 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 image_offset __section(".data");
 static efi_loaded_image_t *image = NULL;
 
 static efi_status_t

I assume it has to do with being in .data vs .bss and not being explicitly
cleared with the encryption bit set. With the change to put image_offset in
the .data section, it is read as zero, where as when it was in the .bss
section it was reading "ciphertext".

Thanks,
Tom

> 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