hwrng: core - Remove add_early_randomness

A potential deadlock was reported with the config file at

https://web.archive.org/web/20240522052129/https://0x0.st/XPN_.txt

In this particular configuration, the deadlock doesn't exist because
the warning triggered at a point before modules were even available.
However, the deadlock can be real because any module loaded would
invoke async_synchronize_full.

The issue is spurious for software crypto algorithms which aren't
themselves involved in async probing.  However, it would be hard to
avoid for a PCI crypto driver using async probing.

In this particular call trace, the problem is easily avoided because
the only reason the module is being requested during probing is the
add_early_randomness call in the hwrng core.  This feature is
vestigial since there is now a kernel thread dedicated to doing
exactly this.

So remove add_early_randomness as it is no longer needed.

Reported-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reported-by: Eric Biggers <ebiggers@kernel.org>
Fixes: 1b6d7f9eb150 ("tpm: add session encryption protection to tpm2_get_random()")
Link: https://lore.kernel.org/r/119dc5ed-f159-41be-9dda-1a056f29888d@notapiano/
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index f5c71a617a993108049f12de67234a39405c27c2..4084df65c9fa33b6b43278e151576a1823049394 100644 (file)
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -64,19 +64,6 @@ static size_t rng_buffer_size(void)
        return RNG_BUFFER_SIZE;
 }
 
-static void add_early_randomness(struct hwrng *rng)
-{
-       int bytes_read;
-
-       mutex_lock(&reading_mutex);
-       bytes_read = rng_get_data(rng, rng_fillbuf, 32, 0);
-       mutex_unlock(&reading_mutex);
-       if (bytes_read > 0) {
-               size_t entropy = bytes_read * 8 * rng->quality / 1024;
-               add_hwgenerator_randomness(rng_fillbuf, bytes_read, entropy, false);
-       }
-}
-
 static inline void cleanup_rng(struct kref *kref)
 {
        struct hwrng *rng = container_of(kref, struct hwrng, ref);
@@ -340,13 +327,12 @@ static ssize_t rng_current_store(struct device *dev,
                                 const char *buf, size_t len)
 {
        int err;
-       struct hwrng *rng, *old_rng, *new_rng;
+       struct hwrng *rng, *new_rng;
 
        err = mutex_lock_interruptible(&rng_mutex);
        if (err)
                return -ERESTARTSYS;
 
-       old_rng = current_rng;
        if (sysfs_streq(buf, "")) {
                err = enable_best_rng();
        } else {
@@ -362,11 +348,8 @@ static ssize_t rng_current_store(struct device *dev,
        new_rng = get_current_rng_nolock();
        mutex_unlock(&rng_mutex);
 
-       if (new_rng) {
-               if (new_rng != old_rng)
-                       add_early_randomness(new_rng);
+       if (new_rng)
                put_rng(new_rng);
-       }
 
        return err ? : len;
 }
@@ -544,7 +527,6 @@ int hwrng_register(struct hwrng *rng)
 {
        int err = -EINVAL;
        struct hwrng *tmp;
-       bool is_new_current = false;
 
        if (!rng->name || (!rng->data_read && !rng->read))
                goto out;
@@ -573,25 +555,8 @@ int hwrng_register(struct hwrng *rng)
                err = set_current_rng(rng);
                if (err)
                        goto out_unlock;
-               /* to use current_rng in add_early_randomness() we need
-                * to take a ref
-                */
-               is_new_current = true;
-               kref_get(&rng->ref);
        }
        mutex_unlock(&rng_mutex);
-       if (is_new_current || !rng->init) {
-               /*
-                * Use a new device's input to add some randomness to
-                * the system.  If this rng device isn't going to be
-                * used right away, its init function hasn't been
-                * called yet by set_current_rng(); so only use the
-                * randomness from devices that don't need an init callback
-                */
-               add_early_randomness(rng);
-       }
-       if (is_new_current)
-               put_rng(rng);
        return 0;
 out_unlock:
        mutex_unlock(&rng_mutex);
@@ -602,12 +567,11 @@ EXPORT_SYMBOL_GPL(hwrng_register);
 
 void hwrng_unregister(struct hwrng *rng)
 {
-       struct hwrng *old_rng, *new_rng;
+       struct hwrng *new_rng;
        int err;
 
        mutex_lock(&rng_mutex);
 
-       old_rng = current_rng;
        list_del(&rng->list);
        complete_all(&rng->dying);
        if (current_rng == rng) {
@@ -626,11 +590,8 @@ void hwrng_unregister(struct hwrng *rng)
        } else
                mutex_unlock(&rng_mutex);
 
-       if (new_rng) {
-               if (old_rng != new_rng)
-                       add_early_randomness(new_rng);
+       if (new_rng)
                put_rng(new_rng);
-       }
 
        wait_for_completion(&rng->cleanup_done);
 }