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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2019-04-20 00:09:51 -0400
committerTheodore Ts'o <tytso@mit.edu>2019-04-20 00:09:56 -0400
commitb7d5dc21072cda7124d13eae2aefb7343ef94197 (patch)
tree09d1d9c39c919133652ffcc8509efbf7c3c2cb7d
parent92e507d216139b356a375afbda2824e85235e748 (diff)
random: add a spinlock_t to struct batched_entropy
The per-CPU variable batched_entropy_uXX is protected by get_cpu_var(). This is just a preempt_disable() which ensures that the variable is only from the local CPU. It does not protect against users on the same CPU from another context. It is possible that a preemptible context reads slot 0 and then an interrupt occurs and the same value is read again. The above scenario is confirmed by lockdep if we add a spinlock: | ================================ | WARNING: inconsistent lock state | 5.1.0-rc3+ #42 Not tainted | -------------------------------- | inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. | ksoftirqd/9/56 [HC0[0]:SC1[1]:HE0:SE0] takes: | (____ptrval____) (batched_entropy_u32.lock){+.?.}, at: get_random_u32+0x3e/0xe0 | {SOFTIRQ-ON-W} state was registered at: | _raw_spin_lock+0x2a/0x40 | get_random_u32+0x3e/0xe0 | new_slab+0x15c/0x7b0 | ___slab_alloc+0x492/0x620 | __slab_alloc.isra.73+0x53/0xa0 | kmem_cache_alloc_node+0xaf/0x2a0 | copy_process.part.41+0x1e1/0x2370 | _do_fork+0xdb/0x6d0 | kernel_thread+0x20/0x30 | kthreadd+0x1ba/0x220 | ret_from_fork+0x3a/0x50 … | other info that might help us debug this: | Possible unsafe locking scenario: | | CPU0 | ---- | lock(batched_entropy_u32.lock); | <Interrupt> | lock(batched_entropy_u32.lock); | | *** DEADLOCK *** | | stack backtrace: | Call Trace: … | kmem_cache_alloc_trace+0x20e/0x270 | ipmi_alloc_recv_msg+0x16/0x40 … | __do_softirq+0xec/0x48d | run_ksoftirqd+0x37/0x60 | smpboot_thread_fn+0x191/0x290 | kthread+0xfe/0x130 | ret_from_fork+0x3a/0x50 Add a spinlock_t to the batched_entropy data structure and acquire the lock while accessing it. Acquire the lock with disabled interrupts because this function may be used from interrupt context. Remove the batched_entropy_reset_lock lock. Now that we have a lock for the data scructure, we can access it from a remote CPU. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
-rw-r--r--drivers/char/random.c52
1 files changed, 27 insertions, 25 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 587df86c1661..a42b3d764da8 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2282,8 +2282,8 @@ struct batched_entropy {
u32 entropy_u32[CHACHA_BLOCK_SIZE / sizeof(u32)];
};
unsigned int position;
+ spinlock_t batch_lock;
};
-static rwlock_t batched_entropy_reset_lock = __RW_LOCK_UNLOCKED(batched_entropy_reset_lock);
/*
* Get a random word for internal kernel use only. The quality of the random
@@ -2293,12 +2293,14 @@ static rwlock_t batched_entropy_reset_lock = __RW_LOCK_UNLOCKED(batched_entropy_
* wait_for_random_bytes() should be called and return 0 at least once
* at any point prior.
*/
-static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64);
+static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = {
+ .batch_lock = __SPIN_LOCK_UNLOCKED(batched_entropy_u64.lock),
+};
+
u64 get_random_u64(void)
{
u64 ret;
- bool use_lock;
- unsigned long flags = 0;
+ unsigned long flags;
struct batched_entropy *batch;
static void *previous;
@@ -2313,28 +2315,25 @@ u64 get_random_u64(void)
warn_unseeded_randomness(&previous);
- use_lock = READ_ONCE(crng_init) < 2;
- batch = &get_cpu_var(batched_entropy_u64);
- if (use_lock)
- read_lock_irqsave(&batched_entropy_reset_lock, flags);
+ batch = raw_cpu_ptr(&batched_entropy_u64);
+ spin_lock_irqsave(&batch->batch_lock, flags);
if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
extract_crng((u8 *)batch->entropy_u64);
batch->position = 0;
}
ret = batch->entropy_u64[batch->position++];
- if (use_lock)
- read_unlock_irqrestore(&batched_entropy_reset_lock, flags);
- put_cpu_var(batched_entropy_u64);
+ spin_unlock_irqrestore(&batch->batch_lock, flags);
return ret;
}
EXPORT_SYMBOL(get_random_u64);
-static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32);
+static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
+ .batch_lock = __SPIN_LOCK_UNLOCKED(batched_entropy_u32.lock),
+};
u32 get_random_u32(void)
{
u32 ret;
- bool use_lock;
- unsigned long flags = 0;
+ unsigned long flags;
struct batched_entropy *batch;
static void *previous;
@@ -2343,18 +2342,14 @@ u32 get_random_u32(void)
warn_unseeded_randomness(&previous);
- use_lock = READ_ONCE(crng_init) < 2;
- batch = &get_cpu_var(batched_entropy_u32);
- if (use_lock)
- read_lock_irqsave(&batched_entropy_reset_lock, flags);
+ batch = raw_cpu_ptr(&batched_entropy_u32);
+ spin_lock_irqsave(&batch->batch_lock, flags);
if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0) {
extract_crng((u8 *)batch->entropy_u32);
batch->position = 0;
}
ret = batch->entropy_u32[batch->position++];
- if (use_lock)
- read_unlock_irqrestore(&batched_entropy_reset_lock, flags);
- put_cpu_var(batched_entropy_u32);
+ spin_unlock_irqrestore(&batch->batch_lock, flags);
return ret;
}
EXPORT_SYMBOL(get_random_u32);
@@ -2368,12 +2363,19 @@ static void invalidate_batched_entropy(void)
int cpu;
unsigned long flags;
- write_lock_irqsave(&batched_entropy_reset_lock, flags);
for_each_possible_cpu (cpu) {
- per_cpu_ptr(&batched_entropy_u32, cpu)->position = 0;
- per_cpu_ptr(&batched_entropy_u64, cpu)->position = 0;
+ struct batched_entropy *batched_entropy;
+
+ batched_entropy = per_cpu_ptr(&batched_entropy_u32, cpu);
+ spin_lock_irqsave(&batched_entropy->batch_lock, flags);
+ batched_entropy->position = 0;
+ spin_unlock(&batched_entropy->batch_lock);
+
+ batched_entropy = per_cpu_ptr(&batched_entropy_u64, cpu);
+ spin_lock(&batched_entropy->batch_lock);
+ batched_entropy->position = 0;
+ spin_unlock_irqrestore(&batched_entropy->batch_lock, flags);
}
- write_unlock_irqrestore(&batched_entropy_reset_lock, flags);
}
/**

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