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Kernel: Use RDSEED assembly snippet to seed RNG on Aarch64

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There’s similar RDRAND register (encoded as ‘s3_3_c2_c4_0ʼ) to be
added if needed. RNG CPU feature on Aarch64 guarantees existence of both
RDSEED and RDRAND registers simultaneously—in contrast to x86-64, where
respective instructions are independent of each other.
This commit is contained in:
konrad 2023-01-08 05:30:40 +01:00 committed by Jelle Raaijmakers
parent 7c8e61f4d1
commit e1c50b83e1
Notes: sideshowbarker 2024-07-19 16:57:46 +09:00 
Author: https://github.com/konradekk
Commit: https://github.com/SerenityOS/serenity/commit/e1c50b83e1d
Pull-request: https://github.com/SerenityOS/serenity/pull/17087
Reviewed-by: https://github.com/FireFox317
3 changed files with 26 additions and 0 deletions
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13
Kernel/Arch/aarch64/ASM_wrapper.h
View File

@ -91,6 +91,19 @@ inline void enter_el1_from_el2()
: "x0");
}
inline u64 read_rndrrs()
{
u64 value = 0;
asm volatile(
"retry:\n"
"mrs %[value], s3_3_c2_c4_1 \n" // encoded RNDRRS register
"b.eq retry\n"
: [value] "=r"(value));
return value;
}
}
namespace Kernel {

2
Kernel/Arch/aarch64/Processor.cpp
View File

@ -44,6 +44,8 @@ void Processor::initialize()
dmesgln("CPU[{}]: Supports {}", m_cpu, build_cpu_feature_names(m_features));
dmesgln("CPU[{}]: Physical address bit width: {}", m_cpu, m_physical_address_bit_width);
dmesgln("CPU[{}]: Virtual address bit width: {}", m_cpu, m_virtual_address_bit_width);
if (!has_feature(CPUFeature::RNG))
dmesgln("CPU[{}]: {} not detected, randomness will be poor", m_cpu, cpu_feature_to_description(CPUFeature::RNG));
}
[[noreturn]] void Processor::halt()

11
Kernel/Random.cpp
View File

@ -10,6 +10,8 @@
#if ARCH(X86_64)
# include <Kernel/Arch/x86_64/Time/HPET.h>
# include <Kernel/Arch/x86_64/Time/RTC.h>
#elif ARCH(AARCH64)
# include <Kernel/Arch/aarch64/ASM_wrapper.h>
#endif
#include <Kernel/Devices/RandomDevice.h>
#include <Kernel/Random.h>
@ -59,6 +61,15 @@ UNMAP_AFTER_INIT KernelRng::KernelRng()
current_time += 0x40b2u;
}
}
#elif ARCH(AARCH64)
if (Processor::current().has_feature(CPUFeature::RNG)) {
dmesgln("KernelRng: Using RNDRRS as entropy source");
for (size_t i = 0; i < pool_count * reseed_threshold; ++i) {
add_random_event(Aarch64::Asm::read_rndrrs(), i % 32);
}
} else {
dmesgln("KernelRng: No entropy source available!");
}
#else
dmesgln("KernelRng: No entropy source available!");
#endif