On 2 September 2017 at 07:45, Greg KH [off-list ref] wrote:

On Sat, Aug 19, 2017 at 04:17:40PM +0100, Ard Biesheuvel wrote:

quoted

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 <redacted>
---
 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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
+ *
+ * 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)

idVendor and idProduct are little endian types.

You have run sparse on this code, right?

quoted

+                     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;

Don't we have built-in usb functions for this now?  Why not use them
instead of hand-rolling your own logic?

This is UEFI stub code, which is executed with the kernel image or
decompressor loaded at a completely different address than it was
linked at. Reusing inline functions is usually fine, but anything that
requires linking kernel objects into the decompressor is a bit
cumbersome.

In any case, these patches are RFC only, and it is quite obvious that
having a Chaoskey USB driver in the firmware that produces the
EFI_RNG_PROTOCOL is much better, and the UEFI stub code can just call
into the protocol to get entropy.