Early entropy is hard to come by, especially on non-x86 systems that
lack an architected instruction and are not as uniform as PCs.
Fortunately, on UEFI systems, we can invoke the EFI_RNG_PROTOCOL,
which exposes the platform specific entropy source in a generic way.
We use this protocol to fill the RNG UEFI config table (which is used
during early boot to seed the kernel's entropy pool), and on ARM and
arm64, we invoke it to seed KASLR as well.
Sadly, EFI_RNG_PROTOCOL is not widely implemented, and so it would be
nice to have a fallback for UEFI systems that lack it. So implement
this fallback based on the Chaoskey RNG USB stick, which should be
exposed using the standard UEFI USB I/O protocol if the firmware has
USB support.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
drivers/firmware/efi/Kconfig | 7 ++
drivers/firmware/efi/libstub/Makefile | 2 +-
drivers/firmware/efi/libstub/efistub.h | 3 +
drivers/firmware/efi/libstub/random-chaoskey.c | 126 +++++++++++++++++++++++++
4 files changed, 137 insertions(+), 1 deletion(-)
create mode 100644 drivers/firmware/efi/libstub/random-chaoskey.c
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 2b4c39fdfa91..448a6186d9fb 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -87,6 +87,13 @@ config EFI_RUNTIME_WRAPPERS
config EFI_ARMSTUB
bool
+config EFI_RNG_CHAOSKEY
+ bool "Chaoskey USB RNG support in the UEFI stub"
+ help
+ Fall back to a Chaoskey RNG USB stick in case EFI_RNG_PROTOCOL
+ is not implemented by the firmware. This is used for early
+ seeding of the entropy pool, and for KASLR on ARM and arm64.
+
config EFI_BOOTLOADER_CONTROL
tristate "EFI Bootloader Control"
depends on EFI_VARS
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index dedf9bde44db..fad6bc1d0e2a 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -40,7 +40,7 @@ $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
lib-$(CONFIG_EFI_ARMSTUB) += arm-stub.o fdt.o string.o random.o \
$(patsubst %.c,lib-%.o,$(arm-deps))
-
+lib-$(CONFIG_EFI_RNG_CHAOSKEY) += random-chaoskey.o
lib-$(CONFIG_ARM) += arm32-stub.o
lib-$(CONFIG_ARM64) += arm64-stub.o
CFLAGS_arm64-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index 3afff5facd3b..9579ddb5937d 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -62,6 +62,9 @@ efi_status_t efi_random_alloc(efi_system_table_t *sys_table_arg,
unsigned long size, unsigned long align,
unsigned long *addr, unsigned long random_seed);
+efi_status_t efi_get_random_chaoskey(efi_system_table_t *sys_table_arg,
+ unsigned long size, u8 *out);
+
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);
diff --git a/drivers/firmware/efi/libstub/random-chaoskey.c b/drivers/firmware/efi/libstub/random-chaoskey.c
new file mode 100644
index 000000000000..3f94ec3df9ff
--- /dev/null
+++ b/drivers/firmware/efi/libstub/random-chaoskey.c
@@ -0,0 +1,126 @@
+/*
+ * Copyright (C) 2017 Linaro Ltd; <ard.biesheuvel@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/efi.h>
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+#define CHAOSKEY_VENDOR_ID 0x1d50 /* OpenMoko */
+#define CHAOSKEY_PRODUCT_ID 0x60c6 /* ChaosKey */
+
+static efi_usb_io_protocol_t *chaoskey_usb_io;
+static unsigned long chaoskey_usb_ep_addr, chaoskey_usb_ep_size;
+
+static void locate_chaoskey(efi_system_table_t *sys_table_arg)
+{
+ efi_guid_t usb_io_guid = EFI_USB_IO_PROTOCOL_GUID;
+ unsigned long bufsize = 0, i, j;
+ efi_handle_t *handles;
+ efi_status_t status;
+
+ chaoskey_usb_io = (void *)-1;
+
+ /* find all USB devices that UEFI knows about */
+ status = efi_call_early(locate_handle, EFI_LOCATE_BY_PROTOCOL,
+ &usb_io_guid, NULL, &bufsize, NULL);
+ if (status != EFI_BUFFER_TOO_SMALL)
+ return;
+
+ status = efi_call_early(allocate_pool, EFI_LOADER_DATA, bufsize,
+ (void **)&handles);
+ if (status != EFI_SUCCESS)
+ return;
+
+ status = efi_call_early(locate_handle, EFI_LOCATE_BY_PROTOCOL,
+ &usb_io_guid, NULL, &bufsize, handles);
+ if (status != EFI_SUCCESS)
+ goto out;
+
+ for (i = 0; i < bufsize / sizeof(efi_handle_t); i++) {
+ struct usb_device_descriptor dev;
+ struct usb_interface_descriptor iface;
+ efi_usb_io_protocol_t *p;
+
+ status = efi_call_early(handle_protocol, handles[i],
+ &usb_io_guid, (void **)&p);
+ if (status != EFI_SUCCESS)
+ continue; /* shouldn't happen */
+
+ /* get the device descriptor so we can check the vid/pid */
+ status = p->get_device_descriptor(p, &dev);
+ if (status != EFI_SUCCESS)
+ continue; /* shouldn't happen either */
+
+ if (dev.idVendor != CHAOSKEY_VENDOR_ID ||
+ dev.idProduct != CHAOSKEY_PRODUCT_ID)
+ continue;
+
+ /* get the number of endpoints from the interface descriptor */
+ status = p->get_iface_descriptor(p, &iface);
+ if (status != EFI_SUCCESS)
+ continue;
+
+ /* locate the first BULK IN endpoint */
+ for (j = 0; j < iface.bNumEndpoints; j++) {
+ struct usb_endpoint_descriptor ep;
+
+ status = p->get_ep_descriptor(p, j, &ep);
+ if (status != EFI_SUCCESS)
+ continue;
+
+ if (!usb_endpoint_dir_in(&ep) ||
+ usb_endpoint_type(&ep) != USB_ENDPOINT_XFER_BULK)
+ continue;
+
+ pr_efi(sys_table_arg, "Using ChaosKey for entropy\n");
+
+ chaoskey_usb_io = p;
+ chaoskey_usb_ep_addr = ep.bEndpointAddress;
+ chaoskey_usb_ep_size = usb_endpoint_maxp(&ep);
+
+ goto out;
+ }
+ }
+
+out:
+ efi_call_early(free_pool, handles);
+}
+
+efi_status_t efi_get_random_chaoskey(efi_system_table_t *sys_table_arg,
+ unsigned long size, u8 *out)
+{
+ efi_status_t status;
+
+ if (chaoskey_usb_io == NULL)
+ locate_chaoskey(sys_table_arg);
+ if (chaoskey_usb_io == (void *)-1)
+ return EFI_NOT_FOUND;
+
+ while (size > 0) {
+ u8 buf[chaoskey_usb_ep_size];
+ unsigned long bsize = sizeof(buf);
+ u32 stat;
+
+ status = chaoskey_usb_io->bulk_transfer(chaoskey_usb_io,
+ chaoskey_usb_ep_addr,
+ buf, &bsize, 50, &stat);
+ if (status != EFI_SUCCESS) {
+ pr_efi_err(sys_table_arg,
+ "ChaosKey USB communication failed!\n");
+ return EFI_NOT_FOUND;
+ }
+
+ bsize = min(size, bsize);
+ memcpy(out, buf, bsize);
+ out += bsize;
+ size -= bsize;
+ }
+ return EFI_SUCCESS;
+}
--
2.11.0
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