linux-kernel - [PATCH 5.15 100/145] random: make random_get

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Date:   Fri, 27 May 2022 10:50:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Theodore Tso <tytso@....edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 5.15 100/145] random: make random_get_entropy() return an unsigned long

From: "Jason A. Donenfeld" <Jason@...c4.com>

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@...inikbrodowski.net>
Cc: Theodore Ts'o <tytso@....edu>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -1015,7 +1015,7 @@ 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)
@@ -1046,8 +1046,7 @@ 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);
@@ -1302,8 +1301,7 @@ 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;
@@ -1316,16 +1314,12 @@ 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);
 	}
@@ -1372,7 +1366,7 @@ 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
 
 /*