After 43838a23a05f ("random: fix crng_ready() test") early boot calls to
get_random_bytes() will warn 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.
Test if the crng is initialized before calling get_random_bytes(). If it
is not available then attempt to read from the hardware random generator,
before finally using the TSC.
v2: Add HW random read based on feedback fro h...@zytor.com & ty...@mit.edu
Signed-off-by: Prarit Bhargava <pra...@redhat.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: x...@kernel.org
Cc: "Theodore Ts'o" <ty...@mit.edu>
Cc: Arnd Bergmann <a...@arndb.de>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Rik van Riel <r...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Philippe Ombredanne <pombreda...@nexb.com>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Prarit Bhargava <pra...@redhat.com>
Cc: "Jason A. Donenfeld" <ja...@zx2c4.com>
Cc: Kate Stewart <kstew...@linuxfoundation.org>
---
arch/x86/include/asm/stackprotector.h | 14 +++++++++-----
drivers/char/random.c | 5 ++++-
include/linux/random.h | 1 +
3 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/stackprotector.h
b/arch/x86/include/asm/stackprotector.h
index 8ec97a62c245..082100608d18 100644
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h
@@ -62,17 +62,21 @@ static __always_inline void boot_init_stack_canary(void)
{
u64 canary;
u64 tsc;
+ int ret;
#ifdef CONFIG_X86_64
BUILD_BUG_ON(offsetof(union irq_stack_union, stack_canary) != 40);
#endif
/*
- * We both use the random pool and the current TSC as a source
- * of randomness. The TSC only matters for very early init,
- * there it already has some randomness on most systems. Later
- * on during the bootup the random pool has true entropy too.
+ * During early boot the entropy pool may not be initialized. As an
+ * alternative and if one is available, try to use the hardware random
+ * generator. On most systems the TSC will have some randomness so it
+ * can also be used for entropy during early boot.
*/
- get_random_bytes(&canary, sizeof(canary));
+ if (crng_ready())
+ get_random_bytes(&canary, sizeof(canary));
+ else
+ ret = get_random_bytes_arch(&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 38c6d1af6d1c..ea6466a3ab14 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*CHACHA_KEY_SIZE)
diff --git a/include/linux/random.h b/include/linux/random.h
index 445a0ea4ff49..3b5919cb62ca 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -197,4 +197,5 @@ static inline u32 next_pseudo_random32(u32 seed)
return seed * 1664525 + 1013904223;
}
+extern int crng_ready(void);
#endif /* _LINUX_RANDOM_H */
--
2.17.2
