From: Jason A. Donenfeld <Jason@xxxxxxxxx>
[ Upstream commit d7bf7f3b813e3755226bcb5114ad2ac477514ebf ]
add_latent_entropy() is called every time a process forks, in
kernel_clone(). This in turn calls add_device_randomness() using the
latent entropy global state. add_device_randomness() does two things:
2) Mixes into the input pool the latent entropy argument passed; and
1) Mixes in a cycle counter, a sort of measurement of when the event
took place, the high precision bits of which are presumably
difficult to predict.
(2) is impossible without CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y. But (1) is
always possible. However, currently CONFIG_GCC_PLUGIN_LATENT_ENTROPY=n
disables both (1) and (2), instead of just (2).
This commit causes the CONFIG_GCC_PLUGIN_LATENT_ENTROPY=n case to still
do (1) by passing NULL (len 0) to add_device_randomness() when add_latent_
entropy() is called.
Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Cc: PaX Team <pageexec@xxxxxxxxxxx>
Cc: Emese Revfy <re.emese@xxxxxxxxx>
Fixes: 38addce8b600 ("gcc-plugins: Add latent_entropy plugin")
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/linux/random.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/include/linux/random.h b/include/linux/random.h
index bd954ecbef901..51133627ba73a 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -19,14 +19,14 @@ void add_input_randomness(unsigned int type, unsigned int code,
void add_interrupt_randomness(int irq) __latent_entropy;
void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy);
-#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
static inline void add_latent_entropy(void)
{
+#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
add_device_randomness((const void *)&latent_entropy, sizeof(latent_entropy));
-}
#else
-static inline void add_latent_entropy(void) { }
+ add_device_randomness(NULL, 0);
#endif
+}
#if IS_ENABLED(CONFIG_VMGENID)
void add_vmfork_randomness(const void *unique_vm_id, size_t len);
--
2.39.0
