linux-kernel - [PATCH 4/5] Replace invocation of weak PRNG inside mm/slab

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Date:   Mon, 12 Dec 2022 00:16:07 +0200
From:   david.keisarschm@...l.huji.ac.il
To:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     David <david.keisarschm@...l.huji.ac.il>, aksecurity@...il.com,
        ilay.bahat1@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 4/5] Replace invocation of weak PRNG inside mm/slab_common.c

From: David <david.keisarschm@...l.huji.ac.il>

We changed the invocation
 of prandom_u32_state to get_random_u32.
 We also omitted the initial seeding for the state,
 since get_random_u32 maintains its own,
 so there is no need to keep
storing the state of prandom_u32_state here.

Signed-off-by: David <david.keisarschm@...l.huji.ac.il>
---
 mm/slab_common.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index deb764785..6ac68b9a6 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1130,7 +1130,7 @@ EXPORT_SYMBOL(kmalloc_large_node);
 
 #ifdef CONFIG_SLAB_FREELIST_RANDOM
 /* Randomize a generic freelist */
-static void freelist_randomize(struct rnd_state *state, unsigned int *list,
+static void freelist_randomize(unsigned int *list,
 			       unsigned int count)
 {
 	unsigned int rand;
@@ -1141,7 +1141,7 @@ static void freelist_randomize(struct rnd_state *state, unsigned int *list,
 
 	/* Fisher-Yates shuffle */
 	for (i = count - 1; i > 0; i--) {
-		rand = predictable_rng_prandom_u32_state(state);
+		rand = get_random_u32();
 		rand %= (i + 1);
 		swap(list[i], list[rand]);
 	}
@@ -1151,7 +1151,6 @@ static void freelist_randomize(struct rnd_state *state, unsigned int *list,
 int cache_random_seq_create(struct kmem_cache *cachep, unsigned int count,
 				    gfp_t gfp)
 {
-	struct rnd_state state;
 
 	if (count < 2 || cachep->random_seq)
 		return 0;
@@ -1160,10 +1159,7 @@ int cache_random_seq_create(struct kmem_cache *cachep, unsigned int count,
 	if (!cachep->random_seq)
 		return -ENOMEM;
 
-	/* Get best entropy at this stage of boot */
-	prandom_seed_state(&state, get_random_long());
-
-	freelist_randomize(&state, cachep->random_seq, count);
+	freelist_randomize(cachep->random_seq, count);
 	return 0;
 }
 
-- 
2.38.0