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Date:   Wed, 9 Feb 2022 19:37:05 +0000
From:   Matthew Garrett <mjg59@srcf.ucam.org>
To:     Aditya Garg <gargaditya08@live.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>, Jeremy Kerr <jk@ozlabs.org>,
        "joeyli.kernel@gmail.com" <joeyli.kernel@gmail.com>,
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        "jmorris@namei.org" <jmorris@namei.org>,
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        "dhowells@redhat.com" <dhowells@redhat.com>,
        "jlee@suse.com" <jlee@suse.com>,
        "James.Bottomley@hansenpartnership.com" 
        <James.Bottomley@HansenPartnership.com>,
        "jarkko@kernel.org" <jarkko@kernel.org>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        Orlando Chamberlain <redecorating@protonmail.com>,
        Aun-Ali Zaidi <admin@kodeit.net>
Subject: Re: [PATCH] efi: Do not import certificates from UEFI Secure Boot
 for T2 Macs
Message-ID: <20220209193705.GA15463@srcf.ucam.org>
References: <9D0C961D-9999-4C41-A44B-22FEAF0DAB7F@live.com>
 <20220209164957.GB12763@srcf.ucam.org>
 <5A3C2EBF-13FF-4C37-B2A0-1533A818109F@live.com>
 <20220209183545.GA14552@srcf.ucam.org>
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On Wed, Feb 09, 2022 at 06:35:45PM +0000, Matthew Garrett wrote:

> The LOAD_UEFI_KEYS code isn't doing anything special here - it's just 
> trying to read some variables. If we simply disable that then the 
> expectation would be that reading the same variables from userland would 
> trigger the same failure. So the question is which of the variables that 
> LOAD_UEFI_KEYS accesses is triggering the failure, and what's special 
> about that? If it's a specific variable GUID or name that's failing, we 
> should block that on Apple hardware in order to avoid issues caused by 
> userland performing equivalent accesses.

ie, can you try something like this?

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index f3e54f6616f0..01cbd4811d1e 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -32,6 +32,8 @@
 #include <linux/stringify.h>
 #include <linux/workqueue.h>
 #include <linux/completion.h>
+#include <linux/ucs2_string.h>
+#include <linux/slab.h>
 
 #include <asm/efi.h>
 
@@ -203,6 +205,21 @@ static void efi_call_rts(struct work_struct *work)
 				       (efi_time_t *)arg2);
 		break;
 	case EFI_GET_VARIABLE:
+		unsigned long utf8_name_size;
+		char *utf8_name;
+		char guid_str[sizeof(efi_guid_t)+1];
+
+		utf8_name_size = ucs2_utf8size((efi_char16_t *)arg1);
+		utf8_name = kmalloc(utf8_name_size+1, GFP_KERNEL);
+		if (!utf8_name) {
+			printk(KERN_INFO "failed to allocate UTF8 buffer\n");
+			break;
+		}
+
+		ucs2_as_utf8(utf8_name, (efi_char16_t *)arg1, utf8_name_size + 1);
+		efi_guid_to_str((efi_guid_t *)arg2, guid_str);
+
+		printk(KERN_INFO "Reading EFI variable %s-%s\n", utf8_name, guid_str);
 		status = efi_call_virt(get_variable, (efi_char16_t *)arg1,
 				       (efi_guid_t *)arg2, (u32 *)arg3,
 				       (unsigned long *)arg4, (void *)arg5);