linux-kernel - [PATCH] x86/espfix: Use get_random

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20221029002613.143153-1-Jason@zx2c4.com>
Date:   Sat, 29 Oct 2022 02:26:13 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>
Subject: [PATCH] x86/espfix: Use get_random_long() rather than archrandom

A call is made to arch_get_random_longs() and rdtsc(), rather than just
using get_random_long(), because this was written during a time when
very early boot would give abysmal entropy. These days, a call to
get_random_long() at early boot will incorporate RDRAND, RDTSC, and
more, without having to do anything bespoke.

In fact, the situation is now such that on the majority of x86 systems,
the pool actually is initialized at this point, even though it doesn't
need to be for get_random_long() to still return something better than
what this function currently does.

So simplify this to just call get_random_long() instead.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: H. Peter Anvin <hpa@...or.com>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 arch/x86/kernel/espfix_64.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index 9417d5aa7305..16f9814c9be0 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -94,17 +94,7 @@ static inline unsigned long espfix_base_addr(unsigned int cpu)
 
 static void init_espfix_random(void)
 {
-	unsigned long rand;
-
-	/*
-	 * This is run before the entropy pools are initialized,
-	 * but this is hopefully better than nothing.
-	 */
-	if (!arch_get_random_longs(&rand, 1)) {
-		/* The constant is an arbitrary large prime */
-		rand = rdtsc();
-		rand *= 0xc345c6b72fd16123UL;
-	}
+	unsigned long rand = get_random_long();
 
 	slot_random = rand % ESPFIX_STACKS_PER_PAGE;
 	page_random = (rand / ESPFIX_STACKS_PER_PAGE)
-- 
2.38.1