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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id w207sm3831691pff.93.2019.08.28.10.36.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Aug 2019 10:36:24 -0700 (PDT) Date: Sat, 24 Aug 2019 12:04:01 -0700 From: Kees Cook To: Stephen Boyd Cc: "Theodore Y . Ts'o" , Hsin-Yi Wang , linux-arm-kernel@lists.infradead.org, Russell King , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , "Paul E . McKenney" , Kate Stewart , "David S . Miller" , Viresh Kumar , Marek Szyprowski , Arnd Bergmann , Marc Zyngier , Julien Thierry , Greg Kroah-Hartman , Wei Li , Anders Roxell , Rob Herring , Aaro Koskinen , Daniel Thompson , Tim Chen , Rik van Riel , Waiman Long , Marcelo Tosatti , Peter Zijlstra , Armijn Hemel , Grzegorz Halat , Len Brown , Shaokun Zhang , Mike Rapoport , Guenter Roeck , Andrew Morton , Mathieu Desnoyers , Alexey Dobriyan , Yury Norov , Josh Poimboeuf , Jiri Kosina , Mukesh Ojha , linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 2/3] fdt: add support for rng-seed Message-ID: <201908241203.92CC0BE8@keescook> References: <20190822071522.143986-1-hsinyi@chromium.org> <20190822071522.143986-3-hsinyi@chromium.org> <5d5ed368.1c69fb81.419fc.0803@mx.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5d5ed368.1c69fb81.419fc.0803@mx.google.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 22, 2019 at 10:39:51AM -0700, Stephen Boyd wrote: > 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 > > Reviewed-by: Stephen Boyd > > Reviewed-by: Rob Herring > > --- > > 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 Can this please be a boot param (with the default controlled by the CONFIG)? See how CONFIG_RANDOM_TRUST_CPU is wired up... -Kees > > + 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 -- Kees Cook