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Kernel: Make use of interrupts as an entropy source

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Booting old computers without RDRAND/RDSEED and without a disk makes
the system severely starved for entropy. Uses interrupts as a source
to side-step that issue.

Also warn whenever the system is starved of entropy, because that's
a non-obvious failure mode.
This commit is contained in:
Jean-Baptiste Boric 2021-01-24 18:17:54 +01:00 • committed by Andreas Kling
parent cb89d3b780
commit 7eaefa5aa6
3 changed files with 16 additions and 2 deletions
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4
Kernel/Arch/i386/CPU.cpp
View file

@ -44,6 +44,7 @@
#include <Kernel/Interrupts/UnhandledInterruptHandler.h>
#include <Kernel/KSyms.h>
#include <Kernel/Process.h>
#include <Kernel/Random.h>
#include <Kernel/SpinLock.h>
#include <Kernel/Thread.h>
#include <Kernel/VM/MemoryManager.h>
@ -58,6 +59,8 @@ static Descriptor s_idt[256];
static GenericInterruptHandler* s_interrupt_handler[GENERIC_INTERRUPT_HANDLERS_COUNT];
static EntropySource s_entropy_source_interrupts{EntropySource::Static::Interrupts};
// The compiler can't see the calls to these functions inside assembly.
// Declare them, to avoid dead code warnings.
extern "C" void enter_thread_context(Thread* from_thread, Thread* to_thread);
@ -709,6 +712,7 @@ void handle_interrupt(TrapFrame* trap)
auto& regs = *trap->regs;
ASSERT(regs.isr_number >= IRQ_VECTOR_BASE && regs.isr_number <= (IRQ_VECTOR_BASE + GENERIC_INTERRUPT_HANDLERS_COUNT));
u8 irq = (u8)(regs.isr_number - 0x50);
s_entropy_source_interrupts.add_random_event(irq);
auto* handler = s_interrupt_handler[irq];
ASSERT(handler);
handler->increment_invoking_counter();

3
Kernel/Random.cpp
View file

@ -69,6 +69,7 @@ KernelRng::KernelRng()
void KernelRng::wait_for_entropy()
{
if (!resource().is_ready()) {
dbgln("Entropy starvation...");
m_seed_queue.wait_on({}, "KernelRng");
}
}
@ -80,7 +81,7 @@ void KernelRng::wake_if_ready()
}
}
size_t EntropySource::next_source { 0 };
size_t EntropySource::next_source { static_cast<size_t>(EntropySource::Static::MaxHardcodedSourceIndex) };
void get_good_random_bytes(u8* buffer, size_t buffer_size)
{

11
Kernel/Random.h
View file

@ -147,11 +147,21 @@ class EntropySource {
};
public:
enum class Static : size_t {
Interrupts,
MaxHardcodedSourceIndex,
};
EntropySource()
: m_source(next_source++)
{
}
EntropySource(Static hardcoded_source)
: m_source(static_cast<size_t>(hardcoded_source))
{
}
template<typename T>
void add_random_event(const T& event_data)
{
@ -166,7 +176,6 @@ private:
static size_t next_source;
size_t m_pool { 0 };
size_t m_source;
Lock m_lock;
};
// NOTE: These API's are primarily about expressing intent/needs in the calling code.