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Kernel: Make KernelRng thread-safe

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This adds an optional argument to get_good_random_bytes that can be
used to only return randomness if it doesn't have to block.
Also add a SpinLock around using FortunaPRNG.

Fixes #5132
This commit is contained in:
Tom 2021-01-27 13:16:30 -07:00 • committed by Andreas Kling
parent 8104abf640
commit e2d7945e0c
2 changed files with 77 additions and 25 deletions
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20
Kernel/Random.h
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@ -55,8 +55,11 @@ public:
{
}
void get_random_bytes(u8* buffer, size_t n)
bool get_random_bytes(u8* buffer, size_t n)
{
ScopedSpinLock lock(m_lock);
if (!is_ready())
return false;
if (m_p0_len >= reseed_threshold) {
this->reseed();
}
@ -75,6 +78,7 @@ public:
// Extract a new key from the prng stream.
Bytes key_span = m_key.bytes();
cipher.key_stream(key_span, counter_span, &counter_span);
return true;
}
template<typename T>
@ -94,9 +98,12 @@ public:
[[nodiscard]] bool is_ready() const
{
ASSERT(m_lock.is_locked());
return is_seeded() || m_p0_len >= reseed_threshold;
}
SpinLock<u8>& get_lock() { return m_lock; }
private:
void reseed()
{
@ -121,6 +128,7 @@ private:
size_t m_p0_len { 0 };
ByteBuffer m_key;
HashType m_pools[pool_count];
SpinLock<u8> m_lock;
};
class KernelRng : public Lockable<FortunaPRNG<Crypto::Cipher::AESCipher, Crypto::Hash::SHA256, 256>> {
@ -134,6 +142,8 @@ public:
void wake_if_ready();
SpinLock<u8>& get_lock() { return resource().get_lock(); }
private:
WaitQueue m_seed_queue;
};
@ -165,11 +175,13 @@ public:
template<typename T>
void add_random_event(const T& event_data)
{
auto& kernel_rng = KernelRng::the();
ScopedSpinLock lock(kernel_rng.get_lock());
// We don't lock this because on the off chance a pool is corrupted, entropy isn't lost.
Event<T> event = { read_tsc(), m_source, event_data };
KernelRng::the().resource().add_random_event(event, m_pool);
kernel_rng.resource().add_random_event(event, m_pool);
m_pool++;
KernelRng::the().wake_if_ready();
kernel_rng.wake_if_ready();
}
private:
@ -182,7 +194,7 @@ private:
// The only difference is that get_fast_random is guaranteed not to block.
void get_fast_random_bytes(u8*, size_t);
void get_good_random_bytes(u8*, size_t);
bool get_good_random_bytes(u8*, size_t, bool allow_wait = true, bool fallback_to_fast = true);
template<typename T>
inline T get_fast_random()