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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Richard Fitzgerald <rf@opensource.cirrus.com>,
	kernel test robot <lkp@intel.com>, Petr Mladek <pmladek@suse.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH AUTOSEL 4.9 4/9] random32: Fix implicit truncation warning in prandom_seed_state()
Date: Mon,  5 Jul 2021 11:31:50 -0400	[thread overview]
Message-ID: <20210705153155.1522423-4-sashal@kernel.org> (raw)
In-Reply-To: <20210705153155.1522423-1-sashal@kernel.org>

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


  parent reply	other threads:[~2021-07-05 15:35 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-05 15:31 [PATCH AUTOSEL 4.9 1/9] ACPI: processor idle: Fix up C-state latency if not ordered Sasha Levin
2021-07-05 15:31 ` [PATCH AUTOSEL 4.9 2/9] block_dump: remove block_dump feature in mark_inode_dirty() Sasha Levin
2021-07-05 15:31 ` [PATCH AUTOSEL 4.9 3/9] fs: dlm: cancel work sync othercon Sasha Levin
2021-07-05 15:31 ` Sasha Levin [this message]
2021-07-05 15:31 ` [PATCH AUTOSEL 4.9 5/9] fs: dlm: fix memory leak when fenced Sasha Levin
2021-07-05 15:31 ` [PATCH AUTOSEL 4.9 6/9] ACPI: bus: Call kobject_put() in acpi_init() error path Sasha Levin
2021-07-05 15:31 ` [PATCH AUTOSEL 4.9 7/9] platform/x86: toshiba_acpi: Fix missing error code in toshiba_acpi_setup_keyboard() Sasha Levin
2021-07-05 15:31 ` [PATCH AUTOSEL 4.9 8/9] ACPI: tables: Add custom DSDT file as makefile prerequisite Sasha Levin
2021-07-05 15:31 ` [PATCH AUTOSEL 4.9 9/9] ia64: mca_drv: fix incorrect array size calculation Sasha Levin

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