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Kernel: Make Random work on CPUs without rdrand

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- If rdseed is not available, fallback to rdrand.
- If rdrand is not available, block for entropy, or use insecure prng
  depending on if user wants fast or good random.
This commit is contained in:
Peter Elliott 2020-06-27 11:10:01 -06:00 • committed by Andreas Kling
parent 1eb338ab71
commit e1aef94a40
4 changed files with 71 additions and 12 deletions
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56
Kernel/Random.cpp
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@ -44,24 +44,48 @@ KernelRng& KernelRng::the()
KernelRng::KernelRng()
{
if (g_cpu_supports_rdseed) {
if (g_cpu_supports_rdseed || g_cpu_supports_rdrand) {
for (size_t i = 0; i < resource().pool_count * resource().reseed_threshold; ++i) {
u32 value = 0;
asm volatile(
"1:\n"
"rdseed %0\n"
"jnc 1b\n"
: "=r"(value));
if (g_cpu_supports_rdseed) {
asm volatile(
"1:\n"
"rdseed %0\n"
"jnc 1b\n"
: "=r"(value));
} else {
asm volatile(
"1:\n"
"rdrand %0\n"
"jnc 1b\n"
: "=r"(value));
}
this->resource().add_random_event(value, i % 32);
}
}
}
void KernelRng::wait_for_entropy()
{
if (!resource().is_ready()) {
Thread::current->wait_on(m_seed_queue);
}
}
void KernelRng::wake_if_ready()
{
if (resource().is_ready()) {
m_seed_queue.wake_all();
}
}
size_t EntropySource::next_source { 0 };
void get_good_random_bytes(u8* buffer, size_t buffer_size)
{
KernelRng::the().wait_for_entropy();
// FIXME: What if interrupts are disabled because we're in an interrupt?
if (are_interrupts_enabled()) {
LOCKER(KernelRng::the().lock());
@ -73,7 +97,25 @@ void get_good_random_bytes(u8* buffer, size_t buffer_size)
void get_fast_random_bytes(u8* buffer, size_t buffer_size)
{
return get_good_random_bytes(buffer, buffer_size);
if (KernelRng::the().resource().is_ready()) {
return get_good_random_bytes(buffer, buffer_size);
}
static u32 next = 1;
union {
u8 bytes[4];
u32 value;
} u;
size_t offset = 4;
for (size_t i = 0; i < buffer_size; ++i) {
if (offset >= 4) {
next = next * 1103515245 + 12345;
u.value = next;
offset = 0;
}
buffer[i] = u.bytes[offset++];
}
}
}