On 2 September 2017 at 07:45, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Sat, Aug 19, 2017 at 04:17:40PM +0100, Ard Biesheuvel wrote:
>> 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)
>
> idVendor and idProduct are little endian types.
>
> You have run sparse on this code, right?
>
>
>> + 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.
--
To unsubscribe from this list: send the line "unsubscribe linux-efi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
