From: Hsin-Yi Wang hsinyi@chromium.org
commit 428826f5358c922dc378830a1717b682c0823160 upstream.
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 Reviewed-by: Theodore Ts'o tytso@mit.edu # drivers/char/random.c Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/Kconfig | 9 +++++++++ drivers/char/random.c | 14 ++++++++++++++ drivers/of/fdt.c | 14 ++++++++++++-- include/linux/random.h | 1 + 4 files changed, 36 insertions(+), 2 deletions(-)
--- a/drivers/char/Kconfig +++ b/drivers/char/Kconfig @@ -604,3 +604,12 @@ 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" + help + 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 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -2440,3 +2440,17 @@ void add_hwgenerator_randomness(const ch } } 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) +{ + 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 --- a/drivers/of/fdt.c +++ b/drivers/of/fdt.c @@ -27,6 +27,7 @@ #include <linux/debugfs.h> #include <linux/serial_core.h> #include <linux/sysfs.h> +#include <linux/random.h>
#include <asm/setup.h> /* for COMMAND_LINE_SIZE */ #include <asm/page.h> @@ -1117,6 +1118,7 @@ int __init early_init_dt_scan_chosen(uns { int l; const char *p; + const void *rng_seed;
pr_debug("search "chosen", depth: %d, uname: %s\n", depth, uname);
@@ -1151,6 +1153,14 @@ int __init early_init_dt_scan_chosen(uns
pr_debug("Command line is: %s\n", (char*)data);
+ rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l); + if (rng_seed && l > 0) { + add_bootloader_randomness(rng_seed, l); + + /* try to clear seed so it won't be found. */ + fdt_nop_property(initial_boot_params, node, "rng-seed"); + } + /* break now */ return 1; } @@ -1262,8 +1272,6 @@ bool __init early_init_dt_verify(void *p
/* Setup flat device-tree pointer */ initial_boot_params = params; - of_fdt_crc32 = crc32_be(~0, initial_boot_params, - fdt_totalsize(initial_boot_params)); return true; }
@@ -1289,6 +1297,8 @@ bool __init early_init_dt_scan(void *par return false;
early_init_dt_scan_nodes(); + of_fdt_crc32 = crc32_be(~0, initial_boot_params, + fdt_totalsize(initial_boot_params)); return true; }
--- a/include/linux/random.h +++ b/include/linux/random.h @@ -19,6 +19,7 @@ struct random_ready_callback { };
extern void add_device_randomness(const void *, unsigned int); +extern void add_bootloader_randomness(const void *, unsigned int);
#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__) static inline void add_latent_entropy(void)