On Sat, Sep 02, 2017 at 09:18:34AM +0100, Ard Biesheuvel wrote:
> 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.
So this is not Linux kernel code? Or is it? I'm totally confused now.
> 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.
Ok, why not write that and not have to deal with any Linux code at all?
thanks,
greg k-h
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