Kernel: Make use of interrupts as an entropy source

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.

1 files changed, 4 insertions, 0 deletions

diff --git a/Kernel/Arch/i386/CPU.cpp b/Kernel/Arch/i386/CPU.cpp
index da850af1c3..9a9e1a29af 100644
--- a/Kernel/Arch/i386/CPU.cpp
+++ b/Kernel/Arch/i386/CPU.cpp
@@ -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();