random32: Fix implicit truncation warning in prandom_seed_state()

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

diff --git a/include/linux/prandom.h b/include/linux/prandom.h
index bbf4b4ad61dfda9dc66da325d9a29d3b9e6cbf09..056d31317e4990a6f3f25041be076a9db289d846 100644 (file)
--- a/include/linux/prandom.h
+++ b/include/linux/prandom.h
@@ -111,7 +111,7 @@ 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);