random: Make it work on rt

Delegate the random insertion to the forced threaded interrupt
handler. Store the return IP of the hard interrupt handler in the irq
descriptor and feed it into the random generator as a source of
entropy.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

5 files changed, 19 insertions, 7 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index feae5493af9d..f786798eee85 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -745,18 +745,16 @@ EXPORT_SYMBOL_GPL(add_input_randomness);
 
 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
 
-void add_interrupt_randomness(int irq, int irq_flags)
+void add_interrupt_randomness(int irq, int irq_flags, __u64 ip)
 {
 	struct entropy_store	*r;
 	struct fast_pool	*fast_pool = &__get_cpu_var(irq_randomness);
-	struct pt_regs		*regs = get_irq_regs();
 	unsigned long		now = jiffies;
 	__u32			input[4], cycles = get_cycles();
 
 	input[0] = cycles ^ jiffies;
 	input[1] = irq;
-	if (regs) {
-		__u64 ip = instruction_pointer(regs);
+	if (ip) {
 		input[2] = ip;
 		input[3] = ip >> 32;
 	}
@@ -770,7 +768,11 @@ void add_interrupt_randomness(int irq, int irq_flags)
 	fast_pool->last = now;
 
 	r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;
+#ifndef CONFIG_PREEMPT_RT_FULL
 	__mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
+#else
+	mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
+#endif
 	/*
 	 * If we don't have a valid cycle counter, and we see
 	 * back-to-back timer interrupts, then skip giving credit for
diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index 9a323d12de1c..5bf5addfdc58 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -52,6 +52,7 @@ struct irq_desc {
 	unsigned int		irq_count;	/* For detecting broken IRQs */
 	unsigned long		last_unhandled;	/* Aging timer for unhandled count */
 	unsigned int		irqs_unhandled;
+	u64			random_ip;
 	raw_spinlock_t		lock;
 	struct cpumask		*percpu_enabled;
 #ifdef CONFIG_SMP
diff --git a/include/linux/random.h b/include/linux/random.h
index ac621ce886ca..9ae01e28e826 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -51,7 +51,7 @@ struct rnd_state {
 extern void add_device_randomness(const void *, unsigned int);
 extern void add_input_randomness(unsigned int type, unsigned int code,
 				 unsigned int value);
-extern void add_interrupt_randomness(int irq, int irq_flags);
+extern void add_interrupt_randomness(int irq, int irq_flags, __u64 ip);
 
 extern void get_random_bytes(void *buf, int nbytes);
 extern void get_random_bytes_arch(void *buf, int nbytes);
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 311c4e62d1aa..7f50c558e46b 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -132,6 +132,8 @@ static void irq_wake_thread(struct irq_desc *desc, struct irqaction *action)
 irqreturn_t
 handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
 {
+	struct pt_regs *regs = get_irq_regs();
+	u64 ip = regs ? instruction_pointer(regs) : 0;
 	irqreturn_t retval = IRQ_NONE;
 	unsigned int flags = 0, irq = desc->irq_data.irq;
 
@@ -173,8 +175,9 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
 	} while (action);
 
 #ifndef CONFIG_PREEMPT_RT_FULL
-	/* FIXME: Can we unbreak that ? */
-	add_interrupt_randomness(irq, flags);
+	add_interrupt_randomness(irq, flags, ip);
+#else
+	desc->random_ip = ip;
 #endif
 
 	if (!noirqdebug)
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index af832180b033..8588c8568ba7 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -823,6 +823,12 @@ static int irq_thread(void *data)
 		if (!noirqdebug)
 			note_interrupt(action->irq, desc, action_ret);
 
+#ifdef CONFIG_PREEMPT_RT_FULL
+		migrate_disable();
+		add_interrupt_randomness(action->irq, 0,
+					 desc->random_ip ^ (u64) action);
+		migrate_enable();
+#endif
 		wake_threads_waitq(desc);
 	}