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Message-ID: <9a5d23ee-06d2-82e3-1e32-00367125990d@raspberrypi.com>
Date: Tue, 7 Jun 2022 14:21:25 +0100
From: Phil Elwell <phil@...pberrypi.com>
To: "Jason A. Donenfeld" <Jason@...c4.com>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
LKML <linux-kernel@...r.kernel.org>
Cc: Stephen Boyd <swboyd@...omium.org>,
Ard Biesheuvel <ardb@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Russell King <linux@...linux.org.uk>,
Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v3] random: defer crediting bootloader randomness to
random_init()
Hi Jason,
On 07/06/2022 13:44, Jason A. Donenfeld wrote:
> Stephen reported that a static key warning splat appears during early
> boot on systems that credit randomness from device trees that contain an
> "rng-seed" property, because because setup_machine_fdt() is called
> before jump_label_init() during setup_arch():
>
> static_key_enable_cpuslocked(): static key '0xffffffe51c6fcfc0' used before call to jump_label_init()
> WARNING: CPU: 0 PID: 0 at kernel/jump_label.c:166 static_key_enable_cpuslocked+0xb0/0xb8
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0+ #224 44b43e377bfc84bc99bb5ab885ff694984ee09ff
> pstate: 600001c9 (nZCv dAIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : static_key_enable_cpuslocked+0xb0/0xb8
> lr : static_key_enable_cpuslocked+0xb0/0xb8
> sp : ffffffe51c393cf0
> x29: ffffffe51c393cf0 x28: 000000008185054c x27: 00000000f1042f10
> x26: 0000000000000000 x25: 00000000f10302b2 x24: 0000002513200000
> x23: 0000002513200000 x22: ffffffe51c1c9000 x21: fffffffdfdc00000
> x20: ffffffe51c2f0831 x19: ffffffe51c6fcfc0 x18: 00000000ffff1020
> x17: 00000000e1e2ac90 x16: 00000000000000e0 x15: ffffffe51b710708
> x14: 0000000000000066 x13: 0000000000000018 x12: 0000000000000000
> x11: 0000000000000000 x10: 00000000ffffffff x9 : 0000000000000000
> x8 : 0000000000000000 x7 : 61632065726f6665 x6 : 6220646573752027
> x5 : ffffffe51c641d25 x4 : ffffffe51c13142c x3 : ffff0a00ffffff05
> x2 : 40000000ffffe003 x1 : 00000000000001c0 x0 : 0000000000000065
> Call trace:
> static_key_enable_cpuslocked+0xb0/0xb8
> static_key_enable+0x2c/0x40
> crng_set_ready+0x24/0x30
> execute_in_process_context+0x80/0x90
> _credit_init_bits+0x100/0x154
> add_bootloader_randomness+0x64/0x78
> early_init_dt_scan_chosen+0x140/0x184
> early_init_dt_scan_nodes+0x28/0x4c
> early_init_dt_scan+0x40/0x44
> setup_machine_fdt+0x7c/0x120
> setup_arch+0x74/0x1d8
> start_kernel+0x84/0x44c
> __primary_switched+0xc0/0xc8
> ---[ end trace 0000000000000000 ]---
> random: crng init done
> Machine model: Google Lazor (rev1 - 2) with LTE
>
> A trivial fix went in to address this on arm64, 73e2d827a501 ("arm64:
> Initialize jump labels before setup_machine_fdt()"). But it appears that
> fixing it on other platforms might not be so trivial. And in the past
> there have been problems related to add_bootloader_randomness() being
> called too early in boot for what it needed.
>
> This patch defers all entropy crediting until random_init(), where we
> can be sure that all facilities we need are up and running. It still
> mixes the actual seed immediately, so that it's maximally useful, but
> the crediting doesn't happen until later.
>
> This also has the positive effect of allowing rng_has_arch_random() to
> reflect bootloader randomness.
>
> Fixes: f5bda35fba61 ("random: use static branch for crng_ready()")
> Reported-by: Stephen Boyd <swboyd@...omium.org>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Russell King <linux@...linux.org.uk>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Phil Elwell <phil@...pberrypi.com>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
> drivers/char/random.c | 29 +++++++++++++----------------
> include/linux/random.h | 2 +-
> 2 files changed, 14 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 4862d4d3ec49..ebfec7cbd5e1 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -725,8 +725,9 @@ static void __cold _credit_init_bits(size_t bits)
> **********************************************************************/
>
> static bool used_arch_random;
> -static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
> -static bool trust_bootloader __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER);
> +static bool trust_cpu __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
> +static bool trust_bootloader __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER);
> +static size_t bootloader_seed_bits __initdata;
> static int __init parse_trust_cpu(char *arg)
> {
> return kstrtobool(arg, &trust_cpu);
> @@ -776,7 +777,7 @@ static struct notifier_block pm_notifier = { .notifier_call = random_pm_notifica
> int __init random_init(const char *command_line)
> {
> ktime_t now = ktime_get_real();
> - unsigned int i, arch_bytes;
> + unsigned int i, arch_bits;
> unsigned long entropy;
>
> #if defined(LATENT_ENTROPY_PLUGIN)
> @@ -784,12 +785,12 @@ int __init random_init(const char *command_line)
> _mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
> #endif
>
> - for (i = 0, arch_bytes = BLAKE2S_BLOCK_SIZE;
> + for (i = 0, arch_bits = BLAKE2S_BLOCK_SIZE * 8;
> i < BLAKE2S_BLOCK_SIZE; i += sizeof(entropy)) {
> if (!arch_get_random_seed_long_early(&entropy) &&
> !arch_get_random_long_early(&entropy)) {
> entropy = random_get_entropy();
> - arch_bytes -= sizeof(entropy);
> + arch_bits -= sizeof(entropy) * 8;
> }
> _mix_pool_bytes(&entropy, sizeof(entropy));
> }
> @@ -800,9 +801,10 @@ int __init random_init(const char *command_line)
>
> if (crng_ready())
> crng_reseed();
> - else if (trust_cpu)
> - _credit_init_bits(arch_bytes * 8);
> - used_arch_random = arch_bytes * 8 >= POOL_READY_BITS;
> + else
> + _credit_init_bits((trust_cpu ? arch_bits : 0) +
> + (trust_bootloader ? bootloader_seed_bits : 0));
> + used_arch_random = arch_bits + bootloader_seed_bits >= POOL_READY_BITS;
>
> WARN_ON(register_pm_notifier(&pm_notifier));
>
> @@ -861,17 +863,12 @@ void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy)
> }
> EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
>
> -/*
> - * Handle random seed passed by bootloader, and credit it if
> - * CONFIG_RANDOM_TRUST_BOOTLOADER is set.
> - */
> -void __cold add_bootloader_randomness(const void *buf, size_t len)
> +/* Handle random seed passed by bootloader during init. */
> +void __init add_bootloader_randomness(const void *buf, size_t len)
> {
> mix_pool_bytes(buf, len);
> - if (trust_bootloader)
> - credit_init_bits(len * 8);
> + bootloader_seed_bits = len * 8;
> }
> -EXPORT_SYMBOL_GPL(add_bootloader_randomness);
>
> #if IS_ENABLED(CONFIG_VMGENID)
> static BLOCKING_NOTIFIER_HEAD(vmfork_chain);
> diff --git a/include/linux/random.h b/include/linux/random.h
> index fae0c84027fd..223b4bd584e7 100644
> --- a/include/linux/random.h
> +++ b/include/linux/random.h
> @@ -13,7 +13,7 @@
> struct notifier_block;
>
> void add_device_randomness(const void *buf, size_t len);
> -void add_bootloader_randomness(const void *buf, size_t len);
> +void __init add_bootloader_randomness(const void *buf, size_t len);
> void add_input_randomness(unsigned int type, unsigned int code,
> unsigned int value) __latent_entropy;
> void add_interrupt_randomness(int irq) __latent_entropy;
v3 boots cleanly and with the firmware-provided entropy available from much earlier:
[ 0.056431] random: crng init done
[ 1.991312] bcm2835-rng 3f104000.rng: hwrng registered
For what it's worth, on rpi-5.15.y and 5.15.45:
Tested-by: Phil Elwell <phil@...pberrypi.com>
Note that the patch needs some adjustment for 5.15.
Phil
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