[PATCH 5.4 218/411] efi: Do not import certificates from UEFI Secure Boot for T2 Macs

Greg Kroah-Hartman
2022-06-13T11:27:50Z

From: Aditya Garg <gargaditya08@live.com>

commit 155ca952c7ca19aa32ecfb7373a32bbc2e1ec6eb upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
security/integrity/platform_certs/keyring_handler.h | 8 ++++
security/integrity/platform_certs/load_uefi.c | 33 ++++++++++++++++++++
2 files changed, 41 insertions(+)

--- a/security/integrity/platform_certs/keyring_handler.h
+++ b/security/integrity/platform_certs/keyring_handler.h
@@ -30,3 +30,11 @@ efi_element_handler_t get_handler_for_db
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
--- a/security/integrity/platform_certs/load_uefi.c
+++ b/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 "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.
*
@@ -78,6 +104,13 @@ static int __init load_uefi_certs(void)
unsigned long dbsize = 0, dbxsize = 0, moksize = 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.get_variable)
return false;