Re: [BUG][SEVERE] Enabling EFI runtime services causes panics in the T2 security chip on Macs equipped with it.

[Orlando Chamberlain <redecorating@protonmail.com>]

On Wed, 12 Jan 2022 19:21:55 +1100
"Ard Biesheuvel" <ardb@kernel.org> wrote:
> What we might do is just use EFI 1.10 for all Apple x86 EFI machines.

I have found logs of pre-T2 x86 Macs that have EFI v2.40 but I haven't
heard of them having the issue with writing to nvram:

[    0.000000] efi: EFI v2.40 by Apple
[    0.000000] efi:  ACPI=0x88ffe000  ACPI 2.0=0x88ffe014  SMBIOS=0x88f00000  SMBIOS 3.0=0x88efe000 
[    0.000000] secureboot: Secure boot disabled
[    0.000000] SMBIOS 3.0.0 present.
[    0.000000] DMI: Apple Inc. MacBookPro14,1/Mac-B4831CEBD52A0C4C, BIOS XXX.XXX.XXX.XXX.0 04/24/2020

MacBookPro14,1 [1], and MacBookPro13,1 [2] have EFI v2.40, but
MacBookPro12,1 [3] has v1.10

[1] https://linux-hardware.org/?probe=b1b965bcfa&log=dmesg
[2] https://linux-hardware.org/?probe=df102d9c8c&log=dmesg
[3] https://linux-hardware.org/?probe=ef5195a62e&log=dmesg

I don't know if this would mean the other Macs with EFI v2.40 would lose
any functionality due to a patch like this (I'm not familiar with what
was added to the runtime services between v1.10 and v2.40).

> Please try the below:
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index ae79c3300129..2303f9b06412 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -722,6 +722,13 @@ void __init efi_systab_report_header(const
> efi_table_hdr_t *systab_hdr,
>                 systab_hdr->revision >> 16,
>                 systab_hdr->revision & 0xffff,
>                 vendor);
> +
> +       if (IS_ENABLED(CONFIG_X86_64) &&
> +           systab_hdr->revision > EFI_1_10_SYSTEM_TABLE_REVISION &&
> +           !strcmp(vendor, "Apple")) {
> +               pr_info("Apple EFI Mac detected, using EFI v1.10
> runtime services only\n");
> +               efi.runtime_version = EFI_1_10_SYSTEM_TABLE_REVISION;
> +       }
>  }
> 
>  static __initdata char memory_type_name[][13] = {

This patch makes writing to nvram work for me on MacBookPro16,1

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