[PATCH v3 2/3] efi: qemu: arm64: Add efi_rng_protocol implementation for the platform

[Sughosh Ganu]

On Sat, 28 Dec 2019 at 20:01, Heinrich Schuchardt <xypron.glpk at gmx.de>
wrote:

> On 12/27/19 3:26 PM, Sughosh Ganu wrote:
> > Add support for the EFI_RNG_PROTOCOL routines for the qemu arm64
> > platform. EFI_RNG_PROTOCOL is an uefi boottime service which is
> > invoked by the efi stub in the kernel for getting random seed for
> > kaslr.
> >
> > The routines are platform specific, and use the virtio-rng device on
> > the platform to get random data.
> >
> > The feature can be enabled through the following config
> > CONFIG_EFI_RNG_PROTOCOL
> >
> > Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> > ---
> > Changes since V2:
> > * Based on review comments from Heinrich Schuchardt, the rng drivers
> >    read all the bytes requested in the individual
> >    drivers. Corresponding changes made in getrng routine to remove the
> >    loop to read the bytes requested, since that would be handled in the
> >    drivers.
> >
> >   board/emulation/qemu-arm/qemu-arm.c | 41 +++++++++++++++++++
> >   include/efi_rng.h                   | 32 +++++++++++++++
> >   lib/efi_loader/Kconfig              |  8 ++++
> >   lib/efi_loader/Makefile             |  1 +
> >   lib/efi_loader/efi_rng.c            | 80
> +++++++++++++++++++++++++++++++++++++
> >   5 files changed, 162 insertions(+)
> >   create mode 100644 include/efi_rng.h
> >   create mode 100644 lib/efi_loader/efi_rng.c
> >
>

<snip>


> > diff --git a/lib/efi_loader/efi_rng.c b/lib/efi_loader/efi_rng.c
> > new file mode 100644
> > index 0000000..eb91aa7
> > --- /dev/null
> > +++ b/lib/efi_loader/efi_rng.c
> > @@ -0,0 +1,80 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Copyright (c) 2019, Linaro Limited
> > + */
> > +
> > +#include <common.h>
> > +#include <dm.h>
> > +#include <efi_loader.h>
> > +#include <efi_rng.h>
> > +#include <rng.h>
> > +
> > +DECLARE_GLOBAL_DATA_PTR;
> > +
> > +static efi_status_t EFIAPI rng_getinfo(struct efi_rng_protocol *this,
> > +                                    efi_uintn_t
> *rng_algorithm_list_size,
> > +                                    efi_guid_t *rng_algorithm_list)
> > +{
> > +     efi_guid_t rng_algo_guid = EFI_RNG_ALGORITHM_RAW;
> > +
> > +     EFI_ENTRY("%p, %p, %p", this, rng_algorithm_list_size,
> > +               rng_algorithm_list);
> > +
> > +     if (!this || !rng_algorithm_list_size)
> > +             return EFI_INVALID_PARAMETER;
> > +
> > +     if (!rng_algorithm_list ||
> > +         *rng_algorithm_list_size < sizeof(*rng_algorithm_list)) {
> > +             *rng_algorithm_list_size = sizeof(*rng_algorithm_list);
> > +             return EFI_BUFFER_TOO_SMALL;
> > +     }
> > +
> > +     /*
> > +      * For now, use EFI_RNG_ALGORITHM_RAW as the default
> > +      * algorithm. If a new algorithm gets added in the
> > +      * future through a Kconfig, rng_algo_guid will be set
> > +      * based on that Kconfig option
> > +      */
> > +     *rng_algorithm_list_size = sizeof(*rng_algorithm_list);
> > +     guidcpy(rng_algorithm_list, &rng_algo_guid);
> > +
> > +     return EFI_EXIT(EFI_SUCCESS);
> > +}
> > +
> > +static efi_status_t EFIAPI getrng(struct efi_rng_protocol *this,
> > +                               efi_guid_t *rng_algorithm,
> > +                               efi_uintn_t rng_value_length,
> > +                               uint8_t *rng_value)
> > +{
> > +     int ret;
> > +     struct udevice *dev;
> > +     const efi_guid_t rng_raw_guid = EFI_RNG_ALGORITHM_RAW;
> > +
> > +     EFI_ENTRY("%p, %p, %zu, %p", this, rng_algorithm, rng_value_length,
> > +               rng_value);
> > +
> > +     if (!this || !rng_value || !rng_value_length)
> > +             return EFI_INVALID_PARAMETER;
> > +
> > +     if (rng_algorithm) {
> > +             if (guidcmp(rng_algorithm, &rng_raw_guid))
> > +                     return EFI_UNSUPPORTED;
> > +     }
> > +
> > +     ret = platform_get_rng_device(&dev);
>
> This does not compile for sandbox_defconfig.
>
> You could replace this by:
>
> ret = uclass_get_device(UCLASS_RNG, 0, &dev);
>

Like I had stated in one of my earlier mail, I would prefer having a
platform specific routine for fetching the rng device. For example, on
qemu, where the rng device is the child of a virtio-pci device, the above
logic would not get the rng device without having previously scanned the
virtio devices. Instead, i will add a weak function
platform_get_rng_device, which uses uclass_get_device. Any platform which
has a different topology, can then define it's own platform_get_rng_device
function.

-sughosh