Re: [PATCH v5] efi: Do not import certificates from UEFI Secure Boot for T2 Macs

From: Mimi Zohar <zohar@linux.ibm.com>
To: Aditya Garg <gargaditya08@live.com>,
	"jarkko@kernel.org" <jarkko@kernel.org>,
	"dmitry.kasatkin@gmail.com" <dmitry.kasatkin@gmail.com>,
	"jmorris@namei.org" <jmorris@namei.org>,
	"serge@hallyn.com" <serge@hallyn.com>,
	"ast@kernel.org" <ast@kernel.org>,
	"daniel@iogearbox.net" <daniel@iogearbox.net>,
	"andrii@kernel.org" <andrii@kernel.org>,
	"kafai@fb.com" <kafai@fb.com>,
	"songliubraving@fb.com" <songliubraving@fb.com>,
	"yhs@fb.com" <yhs@fb.com>,
	"john.fastabend@gmail.com" <john.fastabend@gmail.com>,
	"kpsingh@kernel.org" <kpsingh@kernel.org>
Cc: "linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	Orlando Chamberlain <redecorating@protonmail.com>,
	"admin@kodeit.net" <admin@kodeit.net>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v5] efi: Do not import certificates from UEFI Secure Boot for T2 Macs
Date: Thu, 14 Apr 2022 09:30:42 -0400	[thread overview]
Message-ID: <9aca02b10ff179a8297b06df11bde4faa8a39650.camel@linux.ibm.com> (raw)
In-Reply-To: <E9C28706-2546-40BF-B32C-66A047BE9EFB@live.com>

On Wed, 2022-04-13 at 14:04 +0000, Aditya Garg wrote:
> From: Aditya Garg <gargaditya08@live.com>
> 
> On Apple T2 Macs, when Linux reads the db and dbx efi variables to load
> UEFI Secure Boot certificates, a page fault occurs in Apple firmware
> code and EFI services are disabled with the following logs:
> 
> Call Trace:
>  <TASK>
>  page_fault_oops+0x4f/0x2c0
>  ? search_bpf_extables+0x6b/0x80
>  ? search_module_extables+0x50/0x80
>  ? search_exception_tables+0x5b/0x60
>  kernelmode_fixup_or_oops+0x9e/0x110
>  __bad_area_nosemaphore+0x155/0x190
>  bad_area_nosemaphore+0x16/0x20
>  do_kern_addr_fault+0x8c/0xa0
>  exc_page_fault+0xd8/0x180
>  asm_exc_page_fault+0x1e/0x30
> (Removed some logs from here)
>  ? __efi_call+0x28/0x30
>  ? switch_mm+0x20/0x30
>  ? efi_call_rts+0x19a/0x8e0
>  ? process_one_work+0x222/0x3f0
>  ? worker_thread+0x4a/0x3d0
>  ? kthread+0x17a/0x1a0
>  ? process_one_work+0x3f0/0x3f0
>  ? set_kthread_struct+0x40/0x40
>  ? ret_from_fork+0x22/0x30
>  </TASK>
> ---[ end trace 1f82023595a5927f ]---
> efi: Froze efi_rts_wq and disabled EFI Runtime Services
> integrity: Couldn't get size: 0x8000000000000015
> integrity: MODSIGN: Couldn't get UEFI db list
> efi: EFI Runtime Services are disabled!
> integrity: Couldn't get size: 0x8000000000000015
> integrity: Couldn't get UEFI dbx list
> integrity: Couldn't get size: 0x8000000000000015
> integrity: Couldn't get mokx list
> integrity: Couldn't get size: 0x80000000
> 
> This also occurs when some other variables are read (see examples below,
> there are many more), but only when these variables are read at an early
> stage like db and dbx are to load UEFI certs.
> 
> BridgeOSBootSessionUUID-4d1ede05-38c7-4a6a-9cc6-4bcca8b38c14
> KEK-8be4df61-93ca-11d2-aa0d-00e098032b8c
> 
> On these Macs, we skip reading the EFI variables for the UEFI certificates.
> As a result without certificates, secure boot signature verification fails.
> As these Macs have a non-standard implementation of secure boot that only
> uses Apple's and Microsoft's keys (users can't add their own), securely
> booting Linux was never supported on this hardware, so skipping it
> shouldn't cause a regression.

Based on your explanation, there seems to be two issues - inability to
read EFI variables, "users can't add their own" keys.  Neither of which
mean "a non-standard implementation of secure boot".  Please fix the
"cause" and "affect" in the patch description and comments.

thanks,

Mimi