| Message ID | 20201006201808.37665-3-andre.przywara@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] firmware: smccc: Add SMCCC TRNG function call IDs | expand |
On Tue, Oct 06, 2020 at 09:18:08PM +0100, Andre Przywara wrote: > The ARM architected TRNG firmware interface, described in ARM spec > DEN0098[1], defines an ARM SMCCC based interface to a true random number > generator, provided by firmware. > This can be discovered via the SMCCC >=v1.1 interface, and provides > up to 192 bits of entropy per call. Reviewed-by: Mark Brown <broonie@kernel.org>
Hi Andre, On 06/10/2020 21:18, Andre Przywara wrote: > The ARM architected TRNG firmware interface, described in ARM spec > DEN0098[1], defines an ARM SMCCC based interface to a true random number > generator, provided by firmware. > This can be discovered via the SMCCC >=v1.1 interface, and provides > up to 192 bits of entropy per call. > > Hook this SMC call into arm64's arch_get_random_*() implementation, > coming to the rescue when the CPU does not implement the ARM v8.5 RNG > system registers. > > For the detection, we piggy back on the PSCI/SMCCC discovery (which gives > us the conduit to use: hvc or smc), then try to call the > ARM_SMCCC_TRNG_VERSION function, which returns -1 if this interface is > not implemented. > arch/arm64/include/asm/archrandom.h | 83 +++++++++++++++++++++++++---- > 1 file changed, 73 insertions(+), 10 deletions(-) > diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h > index ffb1a40d5475..b6c291c42a48 100644 > --- a/arch/arm64/include/asm/archrandom.h > +++ b/arch/arm64/include/asm/archrandom.h > @@ -7,6 +7,13 @@ > #include <linux/bug.h> > #include <linux/kernel.h> > #include <asm/cpufeature.h> > +#include <linux/arm-smccc.h> > + > +static enum smc_trng_status { > + SMC_TRNG_UNKNOWN, > + SMC_TRNG_NOT_SUPPORTED, > + SMC_TRNG_SUPPORTED > +} smc_trng_status = SMC_TRNG_UNKNOWN; Doesn't this static variable in a header file mean each file that includes this has its own copy? Is that intentional? Thanks, James
On 07/10/2020 15:16, James Morse wrote: Hi, > On 06/10/2020 21:18, Andre Przywara wrote: >> The ARM architected TRNG firmware interface, described in ARM spec >> DEN0098[1], defines an ARM SMCCC based interface to a true random number >> generator, provided by firmware. >> This can be discovered via the SMCCC >=v1.1 interface, and provides >> up to 192 bits of entropy per call. >> >> Hook this SMC call into arm64's arch_get_random_*() implementation, >> coming to the rescue when the CPU does not implement the ARM v8.5 RNG >> system registers. >> >> For the detection, we piggy back on the PSCI/SMCCC discovery (which gives >> us the conduit to use: hvc or smc), then try to call the >> ARM_SMCCC_TRNG_VERSION function, which returns -1 if this interface is >> not implemented. > >> arch/arm64/include/asm/archrandom.h | 83 +++++++++++++++++++++++++---- >> 1 file changed, 73 insertions(+), 10 deletions(-) > >> diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h >> index ffb1a40d5475..b6c291c42a48 100644 >> --- a/arch/arm64/include/asm/archrandom.h >> +++ b/arch/arm64/include/asm/archrandom.h >> @@ -7,6 +7,13 @@ >> #include <linux/bug.h> >> #include <linux/kernel.h> >> #include <asm/cpufeature.h> >> +#include <linux/arm-smccc.h> >> + >> +static enum smc_trng_status { >> + SMC_TRNG_UNKNOWN, >> + SMC_TRNG_NOT_SUPPORTED, >> + SMC_TRNG_SUPPORTED >> +} smc_trng_status = SMC_TRNG_UNKNOWN; > > Doesn't this static variable in a header file mean each file that includes this has its > own copy? Is that intentional? Right, and it's not intentional. It doesn't really break, but since random.h includes archrandom.h, we get an instance everywhere :-( I wasn't too happy with this detection method to begin with (and also not with stuffing everything into a header file), but wanted to accommodate the early case, where PSCI hasn't been initialised yet, and so we don't know the SMCCC conduit. A static key sounds better, but gets a bit hairy with this scenario, I think. Any ideas here? I could copy Ard's solution and introduce random.c, if that makes more sense. Cheers, Andre
On Wed, 7 Oct 2020 at 16:44, André Przywara <andre.przywara@arm.com> wrote: > > On 07/10/2020 15:16, James Morse wrote: > > Hi, > > > On 06/10/2020 21:18, Andre Przywara wrote: > >> The ARM architected TRNG firmware interface, described in ARM spec > >> DEN0098[1], defines an ARM SMCCC based interface to a true random number > >> generator, provided by firmware. > >> This can be discovered via the SMCCC >=v1.1 interface, and provides > >> up to 192 bits of entropy per call. > >> > >> Hook this SMC call into arm64's arch_get_random_*() implementation, > >> coming to the rescue when the CPU does not implement the ARM v8.5 RNG > >> system registers. > >> > >> For the detection, we piggy back on the PSCI/SMCCC discovery (which gives > >> us the conduit to use: hvc or smc), then try to call the > >> ARM_SMCCC_TRNG_VERSION function, which returns -1 if this interface is > >> not implemented. > > > >> arch/arm64/include/asm/archrandom.h | 83 +++++++++++++++++++++++++---- > >> 1 file changed, 73 insertions(+), 10 deletions(-) > > > >> diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h > >> index ffb1a40d5475..b6c291c42a48 100644 > >> --- a/arch/arm64/include/asm/archrandom.h > >> +++ b/arch/arm64/include/asm/archrandom.h > >> @@ -7,6 +7,13 @@ > >> #include <linux/bug.h> > >> #include <linux/kernel.h> > >> #include <asm/cpufeature.h> > >> +#include <linux/arm-smccc.h> > >> + > >> +static enum smc_trng_status { > >> + SMC_TRNG_UNKNOWN, > >> + SMC_TRNG_NOT_SUPPORTED, > >> + SMC_TRNG_SUPPORTED > >> +} smc_trng_status = SMC_TRNG_UNKNOWN; > > > > Doesn't this static variable in a header file mean each file that includes this has its > > own copy? Is that intentional? > > Right, and it's not intentional. It doesn't really break, but since > random.h includes archrandom.h, we get an instance everywhere :-( > > I wasn't too happy with this detection method to begin with (and also > not with stuffing everything into a header file), but wanted to > accommodate the early case, where PSCI hasn't been initialised yet, and > so we don't know the SMCCC conduit. A static key sounds better, but gets > a bit hairy with this scenario, I think. > > Any ideas here? I think the early case isn't worth obsessing about. PSCI is initialized in setup_arch(), which gets called way before rand_initialize(), which is where this functionality will get used the first time typically. And kaslr_early_init() is called extremely early, i.e., straight from head.S, and we should avoid adding any more code there that sets global state (if kaslr_early_init() exits successfully, the kernel will be unmapped and remapped again in a different place, and BSS cleared again etc etc) > I could copy Ard's solution and introduce random.c, if that makes more > sense. > > Cheers, > Andre
diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h index ffb1a40d5475..b6c291c42a48 100644 --- a/arch/arm64/include/asm/archrandom.h +++ b/arch/arm64/include/asm/archrandom.h @@ -7,6 +7,13 @@ #include <linux/bug.h> #include <linux/kernel.h> #include <asm/cpufeature.h> +#include <linux/arm-smccc.h> + +static enum smc_trng_status { + SMC_TRNG_UNKNOWN, + SMC_TRNG_NOT_SUPPORTED, + SMC_TRNG_SUPPORTED +} smc_trng_status = SMC_TRNG_UNKNOWN; static inline bool __arm64_rndr(unsigned long *v) { @@ -26,6 +33,36 @@ static inline bool __arm64_rndr(unsigned long *v) return ok; } +static inline bool __check_smc_trng(void) +{ + struct arm_smccc_res res; + + if (smc_trng_status == SMC_TRNG_UNKNOWN) { + /* + * The variable behind the get_version() call is initialised + * as ARM_SMCCC_VERSION_1_0, so getting this could mean: + * a) not checked yet (early at boot, before PSCI init), or + * b) not implemented by firmware. + * Since we don't know which one it is, we return false, but + * don't fix the answer yet. + */ + if (arm_smccc_get_version() <= ARM_SMCCC_VERSION_1_0) + return false; + + /* + * With the knowledge at having at least SMCCC v1.1, we + * can now test the existence of the interface. + */ + arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_VERSION, &res); + if ((int)res.a0 < 0) + smc_trng_status = SMC_TRNG_NOT_SUPPORTED; + else + smc_trng_status = SMC_TRNG_SUPPORTED; + } + + return smc_trng_status == SMC_TRNG_SUPPORTED; +} + static inline bool __must_check arch_get_random_long(unsigned long *v) { return false; @@ -38,26 +75,52 @@ static inline bool __must_check arch_get_random_int(unsigned int *v) static inline bool __must_check arch_get_random_seed_long(unsigned long *v) { + struct arm_smccc_res res; + /* - * Only support the generic interface after we have detected - * the system wide capability, avoiding complexity with the - * cpufeature code and with potential scheduling between CPUs + * Try the ARMv8.5-A RNDR instruction first, but only after + * we have detected the system wide capability, avoiding complexity + * with the cpufeature code and with potential scheduling between CPUs * with and without the feature. */ - if (!cpus_have_const_cap(ARM64_HAS_RNG)) - return false; + if (cpus_have_const_cap(ARM64_HAS_RNG)) + return __arm64_rndr(v); - return __arm64_rndr(v); -} + if (__check_smc_trng()) { + arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res); + if ((int)res.a0 < 0) + return false; + *v = res.a3; + return true; + } + + return false; +} static inline bool __must_check arch_get_random_seed_int(unsigned int *v) { + struct arm_smccc_res res; unsigned long val; - bool ok = arch_get_random_seed_long(&val); - *v = val; - return ok; + if (cpus_have_const_cap(ARM64_HAS_RNG)) { + if (arch_get_random_seed_long(&val)) { + *v = val; + return true; + } + return false; + } + + if (__check_smc_trng()) { + arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 32, &res); + if ((int)res.a0 < 0) + return false; + + *v = res.a3 & GENMASK(31, 0); + return true; + } + + return false; } static inline bool __init __early_cpu_has_rndr(void)
The ARM architected TRNG firmware interface, described in ARM spec DEN0098[1], defines an ARM SMCCC based interface to a true random number generator, provided by firmware. This can be discovered via the SMCCC >=v1.1 interface, and provides up to 192 bits of entropy per call. Hook this SMC call into arm64's arch_get_random_*() implementation, coming to the rescue when the CPU does not implement the ARM v8.5 RNG system registers. For the detection, we piggy back on the PSCI/SMCCC discovery (which gives us the conduit to use: hvc or smc), then try to call the ARM_SMCCC_TRNG_VERSION function, which returns -1 if this interface is not implemented. [1] https://developer.arm.com/documentation/den0098/latest/ Signed-off-by: Andre Przywara <andre.przywara@arm.com> --- arch/arm64/include/asm/archrandom.h | 83 +++++++++++++++++++++++++---- 1 file changed, 73 insertions(+), 10 deletions(-)