[PATCH v2 3/3] efi-panic: Introduce the UEFI panic notification mechanism

From: Guilherme G. Piccoli
Date: Fri Jul 29 2022 - 15:48:48 EST

Despite we have pstore, kdump and other panic-time mechanisms,
there's no generic way to let the firmware know a panic event
happened. Some hypervisors might have special code for that, but
that's not generic.

The UEFI panic notification module hereby proposed aims to fill
this need: once we face a panic, through the panic notifier
infrastructure we set a UEFI variable named PanicWarn with a
value - default is 0xFF, but it's adjustable via module parameter.
The firmware is then enabled to take a proper action.

The module also let the users know that last execution likely
panicked if the UEFI variable is present on module load - then
it clears that to avoid confusing users, only the last panic
event is recorded.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
---
drivers/firmware/efi/Kconfig | 10 ++++
drivers/firmware/efi/Makefile | 1 +
drivers/firmware/efi/efi-panic.c | 89 ++++++++++++++++++++++++++++++++
include/linux/efi.h | 1 +
4 files changed, 101 insertions(+)
create mode 100644 drivers/firmware/efi/efi-panic.c

diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 6cb7384ad2ac..f1ed6128d623 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -147,6 +147,16 @@ config EFI_BOOTLOADER_CONTROL
bootloader reads this reboot reason and takes particular
action according to its policy.

+config EFI_PANIC_NOTIFIER
+ tristate "UEFI Panic Notifier"
+ depends on EFI
+ default n
+ help
+ With this module, kernel creates the UEFI variable "PanicWarn" if
+ the system faces a panic event. With that, the firmware is entitled
+ to take an action if the last kernel panicked; it also shows a
+ message during boot time if last run faced a panic event.
+
config EFI_CAPSULE_LOADER
tristate "EFI capsule loader"
depends on EFI && !IA64
diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
index 8d151e332584..c7cf3dcb284e 100644
--- a/drivers/firmware/efi/Makefile
+++ b/drivers/firmware/efi/Makefile
@@ -25,6 +25,7 @@ obj-$(CONFIG_EFI_RUNTIME_WRAPPERS) += runtime-wrappers.o
subdir-$(CONFIG_EFI_STUB) += libstub
obj-$(CONFIG_EFI_FAKE_MEMMAP) += fake_map.o
obj-$(CONFIG_EFI_BOOTLOADER_CONTROL) += efibc.o
+obj-$(CONFIG_EFI_PANIC_NOTIFIER) += efi-panic.o
obj-$(CONFIG_EFI_TEST) += test/
obj-$(CONFIG_EFI_DEV_PATH_PARSER) += dev-path-parser.o
obj-$(CONFIG_APPLE_PROPERTIES) += apple-properties.o
diff --git a/drivers/firmware/efi/efi-panic.c b/drivers/firmware/efi/efi-panic.c
new file mode 100644
index 000000000000..02ffa4930039
--- /dev/null
+++ b/drivers/firmware/efi/efi-panic.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * efi-panic: UEFI panic notification mechanism
+ */
+
+#define pr_fmt(fmt) "efi-panic: " fmt
+
+#include <linux/efi.h>
+#include <linux/module.h>
+#include <linux/panic_notifier.h>
+
+#define EFI_PANIC_ATTR (EFI_VARIABLE_NON_VOLATILE |\
+ EFI_VARIABLE_BOOTSERVICE_ACCESS |\
+ EFI_VARIABLE_RUNTIME_ACCESS)
+
+#define EFI_DATA_SIZE (2 * sizeof(efi_char16_t))
+
+static efi_char16_t *panic_warn_name = L"PanicWarn";
+
+static u8 panic_warn_val = 0xFF;
+module_param(panic_warn_val, byte, 0644);
+MODULE_PARM_DESC(panic_warn_val,
+ "Value written to PanicWarn efivar on panic event [default=0xFF]");
+
+static int efi_panic_cb(struct notifier_block *nb, unsigned long ev,
+ void *unused)
+{
+ efi_char16_t val[2];
+ efi_status_t ret;
+
+ efi_str8_to_str16(val, &panic_warn_val, 1);
+ ret = efi.set_variable_nonblocking(panic_warn_name,
+ &LINUX_EFI_PANIC_WARN_GUID,
+ EFI_PANIC_ATTR, EFI_DATA_SIZE,
+ val);
+
+ if (ret != EFI_SUCCESS)
+ pr_err("failed notifying UEFI about the panic (0x%lx)\n", ret);
+
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block efi_panic_notifier = {
+ .notifier_call = efi_panic_cb,
+};
+
+static int __init efi_panic_init(void)
+{
+ unsigned long sz = EFI_DATA_SIZE;
+ u8 data[EFI_DATA_SIZE];
+ efi_status_t ret;
+
+ if (!efi_rt_services_supported(EFI_RT_SUPPORTED_SET_VARIABLE))
+ return -ENODEV;
+
+ ret = efi.get_variable(panic_warn_name, &LINUX_EFI_PANIC_WARN_GUID,
+ NULL, &sz, data);
+
+ if (ret == EFI_SUCCESS) {
+ pr_info("previous kernel (likely) had a panic\n");
+
+ ret = efi.set_variable(panic_warn_name,
+ &LINUX_EFI_PANIC_WARN_GUID,
+ EFI_PANIC_ATTR, 0, NULL);
+ if (ret != EFI_SUCCESS)
+ pr_warn("cannot delete the UEFI variable\n");
+
+ } else {
+ if (ret != EFI_NOT_FOUND)
+ pr_err("can't read the UEFI variable (err=%lx)\n", ret);
+ }
+
+ atomic_notifier_chain_register(&panic_notifier_list,
+ &efi_panic_notifier);
+
+ return 0;
+}
+module_init(efi_panic_init);
+
+static void __exit efi_panic_exit(void)
+{
+ atomic_notifier_chain_unregister(&panic_notifier_list,
+ &efi_panic_notifier);
+}
+module_exit(efi_panic_exit);
+
+MODULE_AUTHOR("Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>");
+MODULE_DESCRIPTION("UEFI Panic Notification Mechanism");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/efi.h b/include/linux/efi.h
index c0ea01be3772..38a5056cc72a 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -367,6 +367,7 @@ void efi_native_runtime_setup(void);
#define EFI_GLOBAL_VARIABLE_GUID EFI_GUID(0x8be4df61, 0x93ca, 0x11d2, 0xaa, 0x0d, 0x00, 0xe0, 0x98, 0x03, 0x2b, 0x8c)
#define UV_SYSTEM_TABLE_GUID EFI_GUID(0x3b13a7d4, 0x633e, 0x11dd, 0x93, 0xec, 0xda, 0x25, 0x56, 0xd8, 0x95, 0x93)
#define LINUX_EFI_CRASH_GUID EFI_GUID(0xcfc8fc79, 0xbe2e, 0x4ddc, 0x97, 0xf0, 0x9f, 0x98, 0xbf, 0xe2, 0x98, 0xa0)
+#define LINUX_EFI_PANIC_WARN_GUID EFI_GUID(0x9e85b665, 0x08d4, 0x42c9, 0x83, 0x24, 0x47, 0xed, 0x5f, 0xe5, 0x0b, 0xf3)
#define LOADED_IMAGE_PROTOCOL_GUID EFI_GUID(0x5b1b31a1, 0x9562, 0x11d2, 0x8e, 0x3f, 0x00, 0xa0, 0xc9, 0x69, 0x72, 0x3b)
#define EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID EFI_GUID(0x9042a9de, 0x23dc, 0x4a38, 0x96, 0xfb, 0x7a, 0xde, 0xd0, 0x80, 0x51, 0x6a)
#define EFI_UGA_PROTOCOL_GUID EFI_GUID(0x982c298b, 0xf4fa, 0x41cb, 0xb8, 0x38, 0x77, 0xaa, 0x68, 0x8f, 0xb8, 0x39)
--
2.37.1