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

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Date:   Tue, 22 Nov 2022 15:50:54 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Ard Biesheuvel <ardb@...nel.org>
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 11/22/22 15:42, Ard Biesheuvel wrote:
> 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?

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.