efi/random: Increase size of firmware supplied randomness

The crng code requires at least 64 bytes (2 * CHACHA20_BLOCK_SIZE)
to complete the fast boot-time init, so provide that many bytes
when invoking UEFI protocols to seed the entropy pool. Also, add
a notice so we can tell from the boot log when the seeding actually
took place.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170825155019.6740-3-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 8 insertions, 7 deletions

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index a32e1460ade8..c8a27a2c30c1 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -541,6 +541,7 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
                         if (seed != NULL) {
                                 add_device_randomness(seed->bits, seed->size);
                                 early_memunmap(seed, sizeof(*seed) + size);
+                                pr_notice("seeding entropy pool\n");
                         } else {
                                 pr_err("Could not map UEFI random seed!\n");
                         }
@@ -900,7 +901,7 @@ static int update_efi_random_seed(struct notifier_block *nb,
 
         seed = memremap(efi.rng_seed, sizeof(*seed), MEMREMAP_WB);
         if (seed != NULL) {
-                size = min(seed->size, 32U);
+                size = min(seed->size, EFI_RANDOM_SEED_SIZE);
                 memunmap(seed);
         } else {
                 pr_err("Could not map UEFI random seed!\n");
diff --git a/drivers/firmware/efi/libstub/random.c b/drivers/firmware/efi/libstub/random.c
index 7e72954d5860..e0e603a89aa9 100644
--- a/drivers/firmware/efi/libstub/random.c
+++ b/drivers/firmware/efi/libstub/random.c
@@ -145,8 +145,6 @@ efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
         return status;
 }
 
-#define RANDOM_SEED_SIZE        32
-
 efi_status_t efi_random_get_seed(efi_system_table_t *sys_table_arg)
 {
         efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
@@ -162,25 +160,25 @@ efi_status_t efi_random_get_seed(efi_system_table_t *sys_table_arg)
                 return status;
 
         status = efi_call_early(allocate_pool, EFI_RUNTIME_SERVICES_DATA,
-                                sizeof(*seed) + RANDOM_SEED_SIZE,
+                                sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
                                 (void **)&seed);
         if (status != EFI_SUCCESS)
                 return status;
 
-        status = rng->get_rng(rng, &rng_algo_raw, RANDOM_SEED_SIZE,
+        status = rng->get_rng(rng, &rng_algo_raw, EFI_RANDOM_SEED_SIZE,
                               seed->bits);
         if (status == EFI_UNSUPPORTED)
                 /*
                  * Use whatever algorithm we have available if the raw algorithm
                  * is not implemented.
                  */
-                status = rng->get_rng(rng, NULL, RANDOM_SEED_SIZE,
+                status = rng->get_rng(rng, NULL, EFI_RANDOM_SEED_SIZE,
                                       seed->bits);
 
         if (status != EFI_SUCCESS)
                 goto err_freepool;
 
-        seed->size = RANDOM_SEED_SIZE;
+        seed->size = EFI_RANDOM_SEED_SIZE;
         status = efi_call_early(install_configuration_table, &rng_table_guid,
                                 seed);
         if (status != EFI_SUCCESS)
diff --git a/include/linux/efi.h b/include/linux/efi.h
index c241acca0b15..33d41df062bc 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1571,6 +1571,8 @@ efi_status_t efi_exit_boot_services(efi_system_table_t *sys_table,
                                     void *priv,
                                     efi_exit_boot_map_processing priv_func);
 
+#define EFI_RANDOM_SEED_SIZE            64U
+
 struct linux_efi_random_seed {
         u32     size;
         u8      bits[];