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    SubjectRe: [PATCH v9 2/3] fdt: add support for rng-seed
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    Quoting Hsin-Yi Wang (2019-08-22 00:15:22)
    > Introducing a chosen node, rng-seed, which is an entropy that can be
    > passed to kernel called very early to increase initial device
    > randomness. Bootloader should provide this entropy and the value is
    > read from /chosen/rng-seed in DT.
    >
    > Obtain of_fdt_crc32 for CRC check after early_init_dt_scan_nodes(),
    > since early_init_dt_scan_chosen() would modify fdt to erase rng-seed.
    >
    > Add a new interface add_bootloader_randomness() for rng-seed use case.
    > Depends on whether the seed is trustworthy, rng seed would be passed to
    > add_hwgenerator_randomness(). Otherwise it would be passed to
    > add_device_randomness(). Decision is controlled by kernel config
    > RANDOM_TRUST_BOOTLOADER.
    >
    > Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
    > Reviewed-by: Stephen Boyd <swboyd@chromium.org>
    > Reviewed-by: Rob Herring <robh@kernel.org>
    > ---
    > Change from v8:
    > * Add a new interface add_bootloader_randomness
    > * Add a new kernel config
    > ---
    > drivers/char/Kconfig | 10 ++++++++++
    > drivers/char/random.c | 15 +++++++++++++++
    > drivers/of/fdt.c | 14 ++++++++++++--
    > include/linux/random.h | 1 +
    > 4 files changed, 38 insertions(+), 2 deletions(-)
    >
    > diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
    > index 96156c729a31..5974a5906fd0 100644
    > --- a/drivers/char/Kconfig
    > +++ b/drivers/char/Kconfig
    > @@ -551,3 +551,13 @@ config RANDOM_TRUST_CPU
    > has not installed a hidden back door to compromise the CPU's
    > random number generation facilities. This can also be configured
    > at boot with "random.trust_cpu=on/off".
    > +
    > +config RANDOM_TRUST_BOOTLOADER
    > + bool "Trust the bootloader to initialize Linux's CRNG"
    > + default n

    You can drop the default.

    > + help
    > + Bootloader could provide rng-seed set in /chosen/rng-seed in DT to help
    > + increase initial device randomness. Assume the entropy provided is
    > + trustworthy, it would be regarded as true hardware RNGs and update the
    > + entropy estimate. Otherwise it would be regarded as device input that
    > + could help mix the entropy pool, but won't be added to actual entropy.

    Maybe reword this to something like:

    Some bootloaders can provide entropy to increase the kernel's
    initial device randomness. Say Y here to assume the entropy
    provided by the booloader is trustworthy so it will be added to
    the kernel's entropy pool. Otherwise, say N here so it will be
    regarded as device input that only mixes the entropy pool.

    > \ No newline at end of file
    > diff --git a/drivers/char/random.c b/drivers/char/random.c
    > index 5d5ea4ce1442..29d3ff3de1e1 100644
    > --- a/drivers/char/random.c
    > +++ b/drivers/char/random.c
    > @@ -2445,3 +2445,18 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
    > credit_entropy_bits(poolp, entropy);
    > }
    > EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
    > +
    > +/* Handle random seed passed by bootloader.
    > + * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
    > + * it would be regarded as device data.
    > + * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
    > + */
    > +void add_bootloader_randomness(const void *buf, unsigned int size)
    > +{
    > +#ifdef CONFIG_RANDOM_TRUST_BOOTLOADER
    > + add_hwgenerator_randomness(buf, size, size * 8);
    > +#else
    > + add_device_randomness(buf, size);
    > +#endif

    Maybe use

    if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
    add_hwgenerator_randomness(buf, size, size * 8);
    else
    add_device_randomness(buf, size);

    > +}
    > +EXPORT_SYMBOL_GPL(add_bootloader_randomness);
    > \ No newline at end of file

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