efi/arm*/libstub: Invoke EFI_RNG_PROTOCOL to seed the UEFI RNG table

Invoke the EFI_RNG_PROTOCOL protocol in the context of the stub and
install the Linux-specific RNG seed UEFI config table. This will be
picked up by the EFI routines in the core kernel to seed the kernel
entropy pool.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20161112213237.8804-6-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 52 insertions, 0 deletions

diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 993aa56..b4f7d78 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -340,6 +340,8 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
 	if (status != EFI_SUCCESS)
 		pr_efi_err(sys_table, "Failed initrd from command line!\n");
 
+	efi_random_get_seed(sys_table);
+
 	new_fdt_addr = fdt_addr;
 	status = allocate_new_fdt_and_exit_boot(sys_table, handle,
 				&new_fdt_addr, dram_base + MAX_FDT_OFFSET,
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index fe1f225..b98824e 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -71,4 +71,6 @@ efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
 
 efi_status_t check_platform_features(efi_system_table_t *sys_table_arg);
 
+efi_status_t efi_random_get_seed(efi_system_table_t *sys_table_arg);
+
 #endif
diff --git a/drivers/firmware/efi/libstub/random.c b/drivers/firmware/efi/libstub/random.c
index f8e2e5a..3a3feac 100644
--- a/drivers/firmware/efi/libstub/random.c
+++ b/drivers/firmware/efi/libstub/random.c
@@ -143,3 +143,51 @@ 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;
+	efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
+	efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
+	struct efi_rng_protocol *rng;
+	struct linux_efi_random_seed *seed;
+	efi_status_t status;
+
+	status = efi_call_early(locate_protocol, &rng_proto, NULL,
+				(void **)&rng);
+	if (status != EFI_SUCCESS)
+		return status;
+
+	status = efi_call_early(allocate_pool, EFI_RUNTIME_SERVICES_DATA,
+				sizeof(*seed) + RANDOM_SEED_SIZE,
+				(void **)&seed);
+	if (status != EFI_SUCCESS)
+		return status;
+
+	status = rng->get_rng(rng, &rng_algo_raw, 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,
+				      seed->bits);
+
+	if (status != EFI_SUCCESS)
+		goto err_freepool;
+
+	seed->size = RANDOM_SEED_SIZE;
+	status = efi_call_early(install_configuration_table, &rng_table_guid,
+				seed);
+	if (status != EFI_SUCCESS)
+		goto err_freepool;
+
+	return EFI_SUCCESS;
+
+err_freepool:
+	efi_call_early(free_pool, seed);
+	return status;
+}