Messages in this thread | | | Subject | Re: [PATCH v9 2/3] fdt: add support for rng-seed | From | Stephen Boyd <> | Date | Thu, 22 Aug 2019 10:39:51 -0700 |
| |
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
| |