efi: Do not import certificates from UEFI Secure Boot for T2 Macs

On Apple T2 Macs, when Linux attempts to read the db and dbx efi variables
at early boot to load UEFI Secure Boot certificates, a page fault occurs
in Apple firmware code and EFI runtime services are disabled with the
following logs:

[Firmware Bug]: Page fault caused by firmware at PA: 0xffffb1edc0068000
WARNING: CPU: 3 PID: 104 at arch/x86/platform/efi/quirks.c:735 efi_crash_gracefully_on_page_fault+0x50/0xf0
(Removed some logs from here)
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

So we avoid reading these UEFI variables and thus prevent the crash.

Cc: stable@vger.kernel.org
Signed-off-by: Aditya Garg <gargaditya08@live.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/platform_certs/keyring_handler.h

@@ -35,3 +35,11 @@ efi_element_handler_t get_handler_for_mok(const efi_guid_t *sig_type);
 efi_element_handler_t get_handler_for_dbx(const efi_guid_t *sig_type);
 
 #endif
+
+#ifndef UEFI_QUIRK_SKIP_CERT
+#define UEFI_QUIRK_SKIP_CERT(vendor, product) \
+		 .matches = { \
+			DMI_MATCH(DMI_BOARD_VENDOR, vendor), \
+			DMI_MATCH(DMI_PRODUCT_NAME, product), \
+		},
+#endif

security/integrity/platform_certs/load_uefi.c

@@ -3,6 +3,7 @@
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/cred.h>
+#include <linux/dmi.h>
 #include <linux/err.h>
 #include <linux/efi.h>
 #include <linux/slab.h>
@@ -12,6 +13,31 @@
 #include "../integrity.h"
 #include "keyring_handler.h"
 
+/*
+ * On T2 Macs reading the db and dbx efi variables to load UEFI Secure Boot
+ * certificates causes occurrence of a page fault in Apple's firmware and
+ * a crash disabling EFI runtime services. The following quirk skips reading
+ * these variables.
+ */
+static const struct dmi_system_id uefi_skip_cert[] = {
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookPro15,1") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookPro15,2") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookPro15,3") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookPro15,4") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookPro16,1") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookPro16,2") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookPro16,3") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookPro16,4") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookAir8,1") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookAir8,2") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacBookAir9,1") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacMini8,1") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "MacPro7,1") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "iMac20,1") },
+	{ UEFI_QUIRK_SKIP_CERT("Apple Inc.", "iMac20,2") },
+	{ }
+};
+
 /*
  * Look to see if a UEFI variable called MokIgnoreDB exists and return true if
  * it does.
@@ -138,6 +164,13 @@ static int __init load_uefi_certs(void)
 	unsigned long dbsize = 0, dbxsize = 0, mokxsize = 0;
 	efi_status_t status;
 	int rc = 0;
+	const struct dmi_system_id *dmi_id;
+
+	dmi_id = dmi_first_match(uefi_skip_cert);
+	if (dmi_id) {
+		pr_err("Reading UEFI Secure Boot Certs is not supported on T2 Macs.\n");
+		return false;
+	}
 
 	if (!efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE))
 		return false;