linux-kernel - [PATCH] x86, random: Fix get_random_bytes() warning in x86 start

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Date:   Tue, 29 May 2018 08:38:00 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Prarit Bhargava <prarit@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        "Theodore Ts'o" <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rik van Riel <riel@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kees Cook <keescook@...omium.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Kate Stewart <kstewart@...uxfoundation.org>
Subject: [PATCH] x86, random: Fix get_random_bytes() warning in x86 start_kernel

After 43838a23a05f ("random: fix crng_ready() test") early boot calls
to get_random_bytes() will warn on each cpu on x86 because the crng
is not initialized.  For example,

random: get_random_bytes called from start_kernel+0x8e/0x587 with crng_init=0

x86 only uses get_random_bytes() for better randomization of the stack
canary value so the warning is of no consequence.

Export crng_ready() for x86 and test if the crng is initialized before
calling get_random_bytes().

Signed-off-by: Prarit Bhargava <prarit@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
Cc: "Theodore Ts'o" <tytso@....edu>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Philippe Ombredanne <pombredanne@...b.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: Kate Stewart <kstewart@...uxfoundation.org>
---
 arch/x86/include/asm/stackprotector.h | 3 ++-
 drivers/char/random.c                 | 5 ++++-
 include/linux/random.h                | 1 +
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index 371b3a4af000..4e2223aa34fc 100644
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h
@@ -72,7 +72,8 @@ static __always_inline void boot_init_stack_canary(void)
 	 * there it already has some randomness on most systems. Later
 	 * on during the bootup the random pool has true entropy too.
 	 */
-	get_random_bytes(&canary, sizeof(canary));
+	if (crng_ready())
+		get_random_bytes(&canary, sizeof(canary));
 	tsc = rdtsc();
 	canary += tsc + (tsc << 32UL);
 	canary &= CANARY_MASK;
diff --git a/drivers/char/random.c b/drivers/char/random.c
index cd888d4ee605..003091d104bf 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -428,7 +428,10 @@ struct crng_state primary_crng = {
  * its value (from 0->1->2).
  */
 static int crng_init = 0;
-#define crng_ready() (likely(crng_init > 1))
+int crng_ready(void)
+{
+	return likely(crng_init > 1);
+}
 static int crng_init_cnt = 0;
 static unsigned long crng_global_init_time = 0;
 #define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)
diff --git a/include/linux/random.h b/include/linux/random.h
index 2ddf13b4281e..45616513abd9 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -196,4 +196,5 @@ static inline u32 next_pseudo_random32(u32 seed)
 	return seed * 1664525 + 1013904223;
 }
 
+extern int crng_ready(void);
 #endif /* _LINUX_RANDOM_H */
-- 
2.14.3