random: add arch_get_random_*long_early()

mainline inclusion
from mainline-v5.6
commit 253d3194
category:bugfix
bugzilla:NA
CVE:NA

-------------------

Some architectures (e.g. arm64) can have heterogeneous CPUs, and the
boot CPU may be able to provide entropy while secondary CPUs cannot. On
such systems, arch_get_random_long() and arch_get_random_seed_long()
will fail unless support for RNG instructions has been detected on all
CPUs. This prevents the boot CPU from being able to provide
(potentially) trusted entropy when seeding the primary CRNG.

To make it possible to seed the primary CRNG from the boot CPU without
adversely affecting the runtime versions of arch_get_random_long() and
arch_get_random_seed_long(), this patch adds new early versions of the
functions used when initializing the primary CRNG.

Default implementations are provided atop of the existing
arch_get_random_long() and arch_get_random_seed_long() so that only
architectures with such constraints need to provide the new helpers.

There should be no functional change as a result of this patch.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20200210130015.17664-3-mark.rutland@arm.comSigned-off-by: NTheodore Ts'o <tytso@mit.edu>

 Conflicts:
	drivers/char/random.c
	include/linux/random.h
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Reviewed-by: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

include/linux/random.h

@@ -7,6 +7,8 @@
 #ifndef _LINUX_RANDOM_H
 #define _LINUX_RANDOM_H
 
+#include <linux/bug.h>
+#include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/once.h>
 
@@ -142,4 +144,24 @@ static inline bool arch_has_random_seed(void)
 }
 #endif
 
+/*
+ * Called from the boot CPU during startup; not valid to call once
+ * secondary CPUs are up and preemption is possible.
+ */
+#ifndef arch_get_random_seed_long_early
+static inline bool __init arch_get_random_seed_long_early(unsigned long *v)
+{
+	WARN_ON(system_state != SYSTEM_BOOTING);
+	return arch_get_random_seed_long(v);
+}
+#endif
+
+#ifndef arch_get_random_long_early
+static inline bool __init arch_get_random_long_early(unsigned long *v)
+{
+	WARN_ON(system_state != SYSTEM_BOOTING);
+	return arch_get_random_long(v);
+}
+#endif
+
 #endif /* _LINUX_RANDOM_H */