From: Mark Rutland <mark.rutland@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Richard Henderson <richard.henderson@linaro.org>,
Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org,
Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: [PATCH v10 2/3] arm64: random: Add data to pool from setup_arch()
Date: Fri, 10 Jan 2020 12:35:12 +0000 [thread overview]
Message-ID: <20200110123512.GB31707@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20200110122341.8445-3-broonie@kernel.org>
On Fri, Jan 10, 2020 at 12:23:40PM +0000, Mark Brown wrote:
> Since the arm64 ARCH_RANDOM implementation is not available until
> cpufeature has determined the system capabilities it can't be used by
> the generic random code to initialize the entropy pool for early use.
> Instead explicitly add some data to the pool from setup_arch() if the
> boot CPU supports v8.5-RNG, this is the point recommended by the generic
> code.
>
> Note that we are only adding data here, it will be mixed into the pool
> but won't be credited as entropy. There are currently no suitable
> interfaces for that at present - extending the random code to provide
> those will be done as a future step. Providing data is better than not
> doing so as it will still provide an increase in variation in the output
> from the random code and there will be no impact on the rate at which
> entropy is credited compared to what we have without this patch.
>
> Signed-off-by: Mark Brown <broonie@kernel.org>
This is certainly better than the current state of things so:
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Thanks,
Mark.
> ---
> arch/arm64/include/asm/archrandom.h | 30 +++++++++++++++++++++++++++++
> arch/arm64/kernel/setup.c | 2 ++
> 2 files changed, 32 insertions(+)
>
> diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
> index 5ea5a1ce5a5f..2eb1db1f0bdf 100644
> --- a/arch/arm64/include/asm/archrandom.h
> +++ b/arch/arm64/include/asm/archrandom.h
> @@ -59,9 +59,39 @@ static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
> return ok;
> }
>
> +static inline bool __init __early_cpu_has_rndr(void)
> +{
> + /* Open code as we run prior to the first call to cpufeature. */
> + unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1);
> + return (ftr >> ID_AA64ISAR0_RNDR_SHIFT) & 0xf;
> +}
> +
> +/*
> + * Our ARCH_RANDOM implementation does not function until relatively
> + * late in the boot when cpufeature has detertmined system
> + * capabilities so the core code can't use arch_get_random*() to
> + * initialize, instead we call this function to inject data from
> + * setup_arch() if the boot CPU supports v8.5-RNG.
> + */
> +static inline void __init arm64_add_early_rndr_entropy(void)
> +{
> + unsigned long val;
> + int i;
> +
> + if (!__early_cpu_has_rndr())
> + return;
> +
> + /* Add multiple values to mirror the generic code. */
> + for (i = 0; i < 16; i++)
> + if (__arm64_rndr(&val))
> + add_device_randomness(&val, sizeof(val));
> +}
> +
> #else
>
> static inline bool __arm64_rndr(unsigned long *v) { return false; }
> +static inline bool __init __early_cpu_has_rndr(void) { return false; }
> +static inline void __init arm64_add_early_rndr_entropy(void) { }
>
> #endif /* CONFIG_ARCH_RANDOM */
> #endif /* _ASM_ARCHRANDOM_H */
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 56f664561754..170842965a32 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -344,6 +344,8 @@ void __init setup_arch(char **cmdline_p)
> /* Init percpu seeds for random tags after cpus are set up. */
> kasan_init_tags();
>
> + arm64_add_early_rndr_entropy();
> +
> #ifdef CONFIG_ARM64_SW_TTBR0_PAN
> /*
> * Make sure init_thread_info.ttbr0 always generates translation
> --
> 2.20.1
>
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next prev parent reply other threads:[~2020-01-10 12:35 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-10 12:23 [PATCH v10 0/3] ARMv8.5-RNG support Mark Brown
2020-01-10 12:23 ` [PATCH v10 1/3] arm64: Implement archrandom.h for ARMv8.5-RNG Mark Brown
2020-01-14 17:44 ` Will Deacon
2020-01-15 7:40 ` Ard Biesheuvel
2020-01-15 9:16 ` Will Deacon
2020-01-15 9:24 ` Ard Biesheuvel
2020-01-15 11:07 ` Mark Brown
2020-01-15 11:16 ` Will Deacon
2020-01-15 14:26 ` Catalin Marinas
2020-01-16 0:23 ` Richard Henderson
2020-01-16 11:02 ` Catalin Marinas
2020-01-16 11:10 ` Ard Biesheuvel
2020-01-16 11:40 ` Catalin Marinas
2020-01-10 12:23 ` [PATCH v10 2/3] arm64: random: Add data to pool from setup_arch() Mark Brown
2020-01-10 12:35 ` Mark Rutland [this message]
2020-01-13 19:09 ` Richard Henderson
2020-01-15 7:48 ` Ard Biesheuvel
2020-01-15 9:16 ` Will Deacon
2020-01-15 9:22 ` Ard Biesheuvel
2020-01-15 10:11 ` Mark Rutland
2020-01-15 14:01 ` Mark Brown
2020-01-15 12:07 ` Mark Brown
2020-01-15 12:42 ` Will Deacon
2020-01-15 13:36 ` Ard Biesheuvel
2020-01-15 17:04 ` Mark Brown
2020-01-16 11:33 ` Will Deacon
2020-01-15 15:40 ` Mark Brown
2020-01-10 12:23 ` [PATCH v10 3/3] arm64: Use v8.5-RNG entropy for KASLR seed Mark Brown
2020-01-10 12:35 ` Mark Rutland
2020-01-13 19:09 ` Richard Henderson
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