Messages in this thread | | | Date | Tue, 7 Jun 2022 13:19:41 +0100 | Subject | Re: [PATCH v2] random: defer crediting bootloader randomness to random_init() | From | Phil Elwell <> |
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Hi Jason,
On 07/06/2022 12:32, 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@chromium.org> > Cc: Ard Biesheuvel <ardb@kernel.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Russell King <linux@armlinux.org.uk> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Phil Elwell <phil@raspberrypi.com> > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > --- > drivers/char/random.c | 11 ++++++----- > include/linux/random.h | 2 +- > 2 files changed, 7 insertions(+), 6 deletions(-) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 4862d4d3ec49..34399e4bad19 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_bytes __initdata; > static int __init parse_trust_cpu(char *arg) > { > return kstrtobool(arg, &trust_cpu); > @@ -793,6 +794,7 @@ int __init random_init(const char *command_line) > } > _mix_pool_bytes(&entropy, sizeof(entropy)); > } > + arch_bytes += bootloader_seed_bytes; > _mix_pool_bytes(&now, sizeof(now)); > _mix_pool_bytes(utsname(), sizeof(*(utsname()))); > _mix_pool_bytes(command_line, strlen(command_line)); > @@ -865,13 +867,12 @@ 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) > +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_bytes = len; > } > -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;
After a trivial merge conflict (into 5.15) was resolved, this patch allows the downstream kernel with CONFIG_RANDOM_TRUST_BOOTLOADER=y to boot cleanly. However, it does delay the initialisation of crng significantly compared to my hack.
With v2: [ 1.981493] bcm2835-rng 3f104000.rng: hwrng registered [ 12.549190] random: crng init done
With the hack: [ 0.000000] random: crng init done [ 1.970662] bcm2835-rng 3f104000.rng: hwrng registered
I'll leave it to others to decide whether or not this is acceptable.
Phil
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