[PATCH v2 5/5] efi: random: refresh non-volatile random seed when RNG is initialized

Jason A. Donenfeld
2022-11-18T13:34:55Z

EFI has a rather unique benefit that it has access to some limited
non-volatile storage, where the kernel can store a random seed. Register
a notification for when the RNG is initialized, and at that point, store
a new random seed.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
drivers/firmware/efi/efi.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index f12cc29bd4b8..f8edf6164833 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -337,6 +337,24 @@ static void __init efi_debugfs_init(void)
static inline void efi_debugfs_init(void) {}
#endif

+static void refresh_nv_rng_seed(struct work_struct *work)
+{
+ u8 seed[EFI_RANDOM_SEED_SIZE];
+
+ get_random_bytes(seed, sizeof(seed));
+ efi.set_variable(LINUX_EFI_RANDOM_NV_SEED_VAR, &LINUX_EFI_RANDOM_SEED_TABLE_GUID,
+ EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS |
+ EFI_VARIABLE_RUNTIME_ACCESS, sizeof(seed), seed);
+ memzero_explicit(seed, sizeof(seed));
+}
+static int refresh_nv_rng_seed_notification(struct notifier_block *nb, unsigned long action, void *data)
+{
+ static DECLARE_WORK(work, refresh_nv_rng_seed);
+ schedule_work(&work);
+ return 0;
+}
+static struct notifier_block refresh_nv_rng_seed_nb = { .notifier_call = refresh_nv_rng_seed_notification };
+
/*
* We register the efi subsystem with the firmware subsystem and the
* efivars subsystem with the efi subsystem, if the system was booted with
@@ -413,6 +431,7 @@ static int __init efisubsys_init(void)
platform_device_register_simple("efi_secret", 0, NULL, 0);
#endif

+ execute_with_initialized_rng(&refresh_nv_rng_seed_nb);
return 0;

err_remove_group:
--
2.38.1