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random: always mix cycle counter in add_latent_entropy()

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[ 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@dominikbrodowski.net>
Cc: PaX Team <pageexec@freemail.hu>
Cc: Emese Revfy <re.emese@gmail.com>
Fixes: 38addce8b600 ("gcc-plugins: Add latent_entropy plugin")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jason A. Donenfeld 2022-06-01 22:45:33 +02:00 committed by Greg Kroah-Hartman
parent d2edb20b00
commit 5456f0d53b
1 changed files with 3 additions and 3 deletions
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6
include/linux/random.h
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@ -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
}
void get_random_bytes(void *buf, size_t len);
size_t __must_check get_random_bytes_arch(void *buf, size_t len);