linux-kernel - [PATCH v2 3/3] Replace invocation of weak PRNG in arch/x86/mm/kaslr.c

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Message-Id: <ae6258c3dd2a769df9c349f0b14de6dadcfa4386.1670890407.git.david.keisarschm@mail.huji.ac.il>
Date:   Tue, 13 Dec 2022 12:34:59 +0200
From:   david.keisarschm@...l.huji.ac.il
To:     linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:     David <david.keisarschm@...l.huji.ac.il>, aksecurity@...il.com,
        ilay.bahat1@...il.com
Subject: [PATCH v2 3/3] Replace invocation of weak PRNG in arch/x86/mm/kaslr.c

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

We changed the invocation
 of prandom_bytes_state which is
 considered weak to get_random_bytes.
 We also omitted the call to the
 seeding function,
 since get_random_bytes matintains
 its own state,
so there is no need for seeding here anymore.
This is important for the memory initial state
randomization.

Signed-off-by: David <david.keisarschm@...l.huji.ac.il>
---
 arch/x86/mm/kaslr.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 0bb083979..9ef8993d5 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -66,7 +66,6 @@ void __init kernel_randomize_memory(void)
 	size_t i;
 	unsigned long vaddr_start, vaddr;
 	unsigned long rand, memory_tb;
-	struct rnd_state rand_state;
 	unsigned long remain_entropy;
 	unsigned long vmemmap_size;
 
@@ -113,8 +112,6 @@ void __init kernel_randomize_memory(void)
 	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
 		remain_entropy -= get_padding(&kaslr_regions[i]);
 
-	prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
-
 	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
 		unsigned long entropy;
 
@@ -123,7 +120,7 @@ void __init kernel_randomize_memory(void)
 		 * available.
 		 */
 		entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
-		prandom_bytes_state(&rand_state, &rand, sizeof(rand));
+		get_random_bytes(&rand, sizeof(rand));
 		entropy = (rand % (entropy + 1)) & PUD_MASK;
 		vaddr += entropy;
 		*kaslr_regions[i].base = vaddr;
-- 
2.38.0