[PATCH 5.4 127/240] random: make random_get_entropy() return an unsigned long

Greg Kroah-Hartman
2022-06-20T13:51:29Z

commit b0c3e796f24b588b862b61ce235d3c9417dc8983 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 20 +++++++-------------
include/linux/timex.h | 2 +-
2 files changed, 8 insertions(+), 14 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1010,7 +1010,7 @@ 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)
@@ -1041,8 +1041,7 @@ 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);
@@ -1297,8 +1296,7 @@ static void mix_interrupt_randomness(str
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;
@@ -1311,16 +1309,12 @@ 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);
}
@@ -1367,7 +1361,7 @@ static void entropy_timer(struct timer_l
static void try_to_generate_entropy(void)
{
struct {
- cycles_t cycles;
+ unsigned long cycles;
struct timer_list timer;
} stack;

--- 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

/*