[PATCH 4.19 085/421] random32: Fix implicit truncation warning in prandom_seed_state()

Greg Kroah-Hartman
2021-07-19T16:07:56Z

From: Richard Fitzgerald <rf@opensource.cirrus.com>

[ Upstream commit d327ea15a305024ef0085252fa3657bbb1ce25f5 ]

sparse generates the following warning:

include/linux/prandom.h:114:45: sparse: sparse: cast truncates bits from
constant value

This is because the 64-bit seed value is manipulated and then placed in a
u32, causing an implicit cast and truncation. A forced cast to u32 doesn't
prevent this warning, which is reasonable because a typecast doesn't prove
that truncation was expected.

Logical-AND the value with 0xffffffff to make explicit that truncation to
32-bit is intended.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210525122012.6336-3-rf@opensource.cirrus.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/prandom.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/prandom.h b/include/linux/prandom.h
index cc1e71334e53..e20339c78a84 100644
--- a/include/linux/prandom.h
+++ b/include/linux/prandom.h
@@ -93,7 +93,7 @@ static inline u32 __seed(u32 x, u32 m)
*/
static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
{
- u32 i = (seed >> 32) ^ (seed << 10) ^ seed;
+ u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;

state->s1 = __seed(i, 2U);
state->s2 = __seed(i, 8U);
--
2.30.2