random: make random_get_entropy() return an unsigned long

Some implementations were returning type `unsigned long`, while others
that fell back to get_cycles() were implicitly returning a `cycles_t` or
an untyped constant int literal. That makes for weird and confusing
code, and basically all code in the kernel already handled it like it
was an `unsigned long`. I recently tried to handle it as the largest
type it could be, a `cycles_t`, but doing so doesn't really help with
much.

Instead let's just make random_get_entropy() return an unsigned long all
the time. This also matches the commonly used `arch_get_random_long()`
function, so now RDRAND and RDTSC return the same sized integer, which
means one can fallback to the other more gracefully.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Theodore Ts'o <tytso@mit.edu>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index df43c5060f00d2ea23758ff5e37a97eea4764772..6b01b2be9dd497cf3ea08eb16f324c41b427976c 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1018,7 +1018,7 @@ int __init rand_initialize(void)
  */
 void add_device_randomness(const void *buf, size_t size)
 {
-       cycles_t cycles = random_get_entropy();
+       unsigned long cycles = random_get_entropy();
        unsigned long flags, now = jiffies;
 
        if (crng_init == 0 && size)
@@ -1049,8 +1049,7 @@ struct timer_rand_state {
  */
 static void add_timer_randomness(struct timer_rand_state *state, unsigned int num)
 {
-       cycles_t cycles = random_get_entropy();
-       unsigned long flags, now = jiffies;
+       unsigned long cycles = random_get_entropy(), now = jiffies, flags;
        long delta, delta2, delta3;
 
        spin_lock_irqsave(&input_pool.lock, flags);
@@ -1339,8 +1338,7 @@ static void mix_interrupt_randomness(struct work_struct *work)
 void add_interrupt_randomness(int irq)
 {
        enum { MIX_INFLIGHT = 1U << 31 };
-       cycles_t cycles = random_get_entropy();
-       unsigned long now = jiffies;
+       unsigned long cycles = random_get_entropy(), now = jiffies;
        struct fast_pool *fast_pool = this_cpu_ptr(&irq_randomness);
        struct pt_regs *regs = get_irq_regs();
        unsigned int new_count;
@@ -1353,16 +1351,12 @@ void add_interrupt_randomness(int irq)
        if (cycles == 0)
                cycles = get_reg(fast_pool, regs);
 
-       if (sizeof(cycles) == 8)
+       if (sizeof(unsigned long) == 8) {
                irq_data.u64[0] = cycles ^ rol64(now, 32) ^ irq;
-       else {
+               irq_data.u64[1] = regs ? instruction_pointer(regs) : _RET_IP_;
+       } else {
                irq_data.u32[0] = cycles ^ irq;
                irq_data.u32[1] = now;
-       }
-
-       if (sizeof(unsigned long) == 8)
-               irq_data.u64[1] = regs ? instruction_pointer(regs) : _RET_IP_;
-       else {
                irq_data.u32[2] = regs ? instruction_pointer(regs) : _RET_IP_;
                irq_data.u32[3] = get_reg(fast_pool, regs);
        }
@@ -1409,7 +1403,7 @@ static void entropy_timer(struct timer_list *t)
 static void try_to_generate_entropy(void)
 {
        struct {
-               cycles_t cycles;
+               unsigned long cycles;
                struct timer_list timer;
        } stack;
 

diff --git a/include/linux/timex.h b/include/linux/timex.h
index 059b18eb1f1fab1c3af72b9369273a2782ba641d..5745c90c880054ac2a734d43142f8aa4d81431e5 100644 (file)
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -75,7 +75,7 @@
  * By default we use get_cycles() for this purpose, but individual
  * architectures may override this in their asm/timex.h header file.
  */
-#define random_get_entropy()   get_cycles()
+#define random_get_entropy()   ((unsigned long)get_cycles())
 #endif
 
 /*