| Message ID | 20190822071522.143986-3-hsinyi@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | add support for rng-seed | expand |
On Thu, Aug 22, 2019 at 03:15:22PM +0800, Hsin-Yi Wang wrote: > 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> For the changes to drivers/char/random.c: Reviewed-by: Theodore Ts'o <tytso@mit.edu>
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
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 <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 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
On Thu, Aug 29, 2019 at 1:36 AM Kees Cook <keescook@chromium.org> wrote: > > Can this please be a boot param (with the default controlled by the > CONFIG)? See how CONFIG_RANDOM_TRUST_CPU is wired up... > > -Kees > Currently rng-seed read and added in setup_arch() --> setup_machine_fdt().. -> early_init_dt_scan_chosen(), which is earlier than parse_early_param() that initializes early_param. If we want to set it as a boot param, add_bootloader_randomness() can only be called after parse_early_param(). The seed can't be directly added to pool after it's read in. We need to store into global variable and load it later. If this seems okay then I'll add a patch for this. Thanks --- a/drivers/of/fdt.c +++ b/drivers/of/fdt.c @@ -1096,13 +1096,15 @@ static const char *config_cmdline = CONFIG_CMDLINE; +const void* rng_seed; +int rng_seed_len; + int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, int depth, void *data) { int l = 0; const char *p = NULL; char *cmdline = data; - const void *rng_seed; pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname); @@ -1137,10 +1139,8 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, 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); // Originally it's added to entropy pool here - + rng_seed = of_get_flat_dt_prop(node, "rng-seed", &rng_seed_len); + if (rng_seed && rng_seed_len > 0) { /* try to clear seed so it won't be found. */ diff --git a/include/linux/random.h b/include/linux/random.h index 831a002a1882..946840bba7c1 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -31,6 +31,15 @@ static inline void add_latent_entropy(void) static inline void add_latent_entropy(void) {} #endif +extern const void* rng_seed; +extern int rng_seed_len; + +static inline void add_bootloader_entropy(void) +{ + if (rng_seed && rng_seed_len > 0) + add_bootloader_randomness(rng_seed, rng_seed_len); +} + extern void add_input_randomness(unsigned int type, unsigned int code, unsigned int value) __latent_entropy; extern void add_interrupt_randomness(int irq, int irq_flags) __latent_entropy; diff --git a/init/main.c b/init/main.c index 71847af32e4e..f74a8c7b34af 100644 --- a/init/main.c +++ b/init/main.c @@ -645,6 +645,7 @@ asmlinkage __visible void __init start_kernel(void) * - adding command line entropy */ rand_initialize(); + add_bootloader_entropy(); add_latent_entropy(); add_device_randomness(command_line, strlen(command_line)); boot_init_stack_canary();
On Thu, Aug 29, 2019 at 06:03:57PM +0800, Hsin-Yi Wang wrote: > On Thu, Aug 29, 2019 at 1:36 AM Kees Cook <keescook@chromium.org> wrote: > > > > Can this please be a boot param (with the default controlled by the > > CONFIG)? See how CONFIG_RANDOM_TRUST_CPU is wired up... > > > > Currently rng-seed read and added in setup_arch() --> > setup_machine_fdt().. -> early_init_dt_scan_chosen(), which is earlier > than parse_early_param() that initializes early_param. > > If we want to set it as a boot param, add_bootloader_randomness() can > only be called after parse_early_param(). The seed can't be directly > added to pool after it's read in. We need to store into global > variable and load it later. > If this seems okay then I'll add a patch for this. Thanks I thought about asking for this, but we really want to do this as early as possible, so that it can be used by KASLR and other services that are run super early. Also, whether or not we can trust the bootloader is going to be a system-level thing. This should probably be defaulted to off, and only enabled by the system integrator if they are 100%, positively sure, that the entire system is one where we can trust the source of randomness which the bootloader is using --- or for that matter, that the bootloader is trustworthy! Is it really going to be that useful for a random system administrator to be able to flip this on or off from the command line? Hopefully there will be an easy way to configure the firmware or the bootloader to simply not supply entropy, if for some reason it's not trustworthy. - Ted
On Thu, Aug 29, 2019 at 06:03:57PM +0800, Hsin-Yi Wang wrote: > On Thu, Aug 29, 2019 at 1:36 AM Kees Cook <keescook@chromium.org> wrote: > > > > Can this please be a boot param (with the default controlled by the > > CONFIG)? See how CONFIG_RANDOM_TRUST_CPU is wired up... > > > > -Kees > > > > Currently rng-seed read and added in setup_arch() --> > setup_machine_fdt().. -> early_init_dt_scan_chosen(), which is earlier > than parse_early_param() that initializes early_param. > > If we want to set it as a boot param, add_bootloader_randomness() can > only be called after parse_early_param(). The seed can't be directly > added to pool after it's read in. We need to store into global > variable and load it later. > If this seems okay then I'll add a patch for this. Thanks This seems like a good idea to me. > > --- a/drivers/of/fdt.c > +++ b/drivers/of/fdt.c > @@ -1096,13 +1096,15 @@ static const char *config_cmdline = CONFIG_CMDLINE; > > +const void* rng_seed; > +int rng_seed_len; These should be __initdata, yes? > + > int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, > int depth, > void *data) > { > int l = 0; > const char *p = NULL; > char *cmdline = data; > - const void *rng_seed; > > pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname); > > @@ -1137,10 +1139,8 @@ int __init early_init_dt_scan_chosen(unsigned > long node, const char *uname, > > 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); // > Originally it's added to entropy pool here > - > + rng_seed = of_get_flat_dt_prop(node, "rng-seed", &rng_seed_len); > + if (rng_seed && rng_seed_len > 0) { > /* try to clear seed so it won't be found. */ > > diff --git a/include/linux/random.h b/include/linux/random.h > index 831a002a1882..946840bba7c1 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -31,6 +31,15 @@ static inline void add_latent_entropy(void) > static inline void add_latent_entropy(void) {} > #endif > > +extern const void* rng_seed; > +extern int rng_seed_len; > + > +static inline void add_bootloader_entropy(void) > +{ > + if (rng_seed && rng_seed_len > 0) > + add_bootloader_randomness(rng_seed, rng_seed_len); > +} And this should be __init > + > extern void add_input_randomness(unsigned int type, unsigned int code, > unsigned int value) __latent_entropy; > extern void add_interrupt_randomness(int irq, int irq_flags) __latent_entropy; > diff --git a/init/main.c b/init/main.c > index 71847af32e4e..f74a8c7b34af 100644 > --- a/init/main.c > +++ b/init/main.c > @@ -645,6 +645,7 @@ asmlinkage __visible void __init start_kernel(void) > * - adding command line entropy > */ > rand_initialize(); > + add_bootloader_entropy(); > add_latent_entropy(); > add_device_randomness(command_line, strlen(command_line)); > boot_init_stack_canary(); But yeah, looks reasonable to me.
On Thu, Aug 29, 2019 at 11:45:05AM -0400, Theodore Y. Ts'o wrote: > I thought about asking for this, but we really want to do this as > early as possible, so that it can be used by KASLR and other services KASLR entropy is sent via a separate DT entry, since it's needed before the kernel is even running. > that are run super early. Also, whether or not we can trust the Are there things using the kernel RNG before the stack canary is set up? I tried to move all of that code as early as possible already. > bootloader is going to be a system-level thing. This should probably > be defaulted to off, and only enabled by the system integrator if they > are 100%, positively sure, that the entire system is one where we can > trust the source of randomness which the bootloader is using --- or > for that matter, that the bootloader is trustworthy! > > Is it really going to be that useful for a random system administrator > to be able to flip this on or off from the command line? Hopefully > there will be an easy way to configure the firmware or the bootloader > to simply not supply entropy, if for some reason it's not trustworthy. You have a point about bootloader vs system design. I'm cautiously convinced we don't need a boot param, but if we CAN put all the entropy collection in a single place, that'd be nice.
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 + 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. \ 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 +} +EXPORT_SYMBOL_GPL(add_bootloader_randomness); \ No newline at end of file diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c index 9cdf14b9aaab..7d97ab6d0e31 100644 --- a/drivers/of/fdt.c +++ b/drivers/of/fdt.c @@ -24,6 +24,7 @@ #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> @@ -1044,6 +1045,7 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, { int l; const char *p; + const void *rng_seed; pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname); @@ -1078,6 +1080,14 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, 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; } @@ -1166,8 +1176,6 @@ bool __init early_init_dt_verify(void *params) /* 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; } @@ -1197,6 +1205,8 @@ bool __init early_init_dt_scan(void *params) return false; early_init_dt_scan_nodes(); + of_fdt_crc32 = crc32_be(~0, initial_boot_params, + fdt_totalsize(initial_boot_params)); return true; } diff --git a/include/linux/random.h b/include/linux/random.h index 1f7dced2bba6..f189c927fdea 100644 --- 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)