1 files changed, 143 insertions, 0 deletions
diff --git a/drivers/firmware/efi/libstub/random.c b/drivers/firmware/efi/libstub/random.c
new file mode 100644
index 000000000..f85d2c066
--- /dev/null
+++ b/drivers/firmware/efi/libstub/random.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2016 Linaro Ltd;  <ard.biesheuvel@linaro.org>
+ */
+
+#include <linux/efi.h>
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+typedef union efi_rng_protocol efi_rng_protocol_t;
+
+union efi_rng_protocol {
+	struct {
+		efi_status_t (__efiapi *get_info)(efi_rng_protocol_t *,
+						  unsigned long *,
+						  efi_guid_t *);
+		efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *,
+						 efi_guid_t *, unsigned long,
+						 u8 *out);
+	};
+	struct {
+		u32 get_info;
+		u32 get_rng;
+	} mixed_mode;
+};
+
+/**
+ * efi_get_random_bytes() - fill a buffer with random bytes
+ * @size:	size of the buffer
+ * @out:	caller allocated buffer to receive the random bytes
+ *
+ * The call will fail if either the firmware does not implement the
+ * EFI_RNG_PROTOCOL or there are not enough random bytes available to fill
+ * the buffer.
+ *
+ * Return:	status code
+ */
+efi_status_t efi_get_random_bytes(unsigned long size, u8 *out)
+{
+	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
+	efi_status_t status;
+	efi_rng_protocol_t *rng = NULL;
+
+	status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
+	if (status != EFI_SUCCESS)
+		return status;
+
+	return efi_call_proto(rng, get_rng, NULL, size, out);
+}
+
+/**
+ * efi_random_get_seed() - provide random seed as configuration table
+ *
+ * The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are
+ * saved as a configuration table which can be used as entropy by the kernel
+ * for the initialization of its pseudo random number generator.
+ *
+ * If the EFI_RNG_PROTOCOL is not available or there are not enough random bytes
+ * available, the configuration table will not be installed and an error code
+ * will be returned.
+ *
+ * Return:	status code
+ */
+efi_status_t efi_random_get_seed(void)
+{
+	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 linux_efi_random_seed *prev_seed, *seed = NULL;
+	int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE;
+	efi_rng_protocol_t *rng = NULL;
+	efi_status_t status;
+
+	status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
+	if (status != EFI_SUCCESS)
+		return status;
+
+	/*
+	 * Check whether a seed was provided by a prior boot stage. In that
+	 * case, instead of overwriting it, let's create a new buffer that can
+	 * hold both, and concatenate the existing and the new seeds.
+	 * Note that we should read the seed size with caution, in case the
+	 * table got corrupted in memory somehow.
+	 */
+	prev_seed = get_efi_config_table(LINUX_EFI_RANDOM_SEED_TABLE_GUID);
+	if (prev_seed && prev_seed->size <= 512U) {
+		prev_seed_size = prev_seed->size;
+		seed_size += prev_seed_size;
+	}
+
+	/*
+	 * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
+	 * allocation will survive a kexec reboot (although we refresh the seed
+	 * beforehand)
+	 */
+	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
+			     struct_size(seed, bits, seed_size),
+			     (void **)&seed);
+	if (status != EFI_SUCCESS) {
+		efi_warn("Failed to allocate memory for RNG seed.\n");
+		goto err_warn;
+	}
+
+	status = efi_call_proto(rng, get_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 = efi_call_proto(rng, get_rng, NULL,
+					EFI_RANDOM_SEED_SIZE, seed->bits);
+
+	if (status != EFI_SUCCESS)
+		goto err_freepool;
+
+	seed->size = seed_size;
+	if (prev_seed_size)
+		memcpy(seed->bits + EFI_RANDOM_SEED_SIZE, prev_seed->bits,
+		       prev_seed_size);
+
+	status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
+	if (status != EFI_SUCCESS)
+		goto err_freepool;
+
+	if (prev_seed_size) {
+		/* wipe and free the old seed if we managed to install the new one */
+		memzero_explicit(prev_seed->bits, prev_seed_size);
+		efi_bs_call(free_pool, prev_seed);
+	}
+	return EFI_SUCCESS;
+
+err_freepool:
+	memzero_explicit(seed, struct_size(seed, bits, seed_size));
+	efi_bs_call(free_pool, seed);
+	efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL\n");
+err_warn:
+	if (prev_seed)
+		efi_warn("Retaining bootloader-supplied seed only");
+	return status;
+}