random: handle archrandom with multiple longs

The archrandom interface was originally designed for x86, which supplies
RDRAND/RDSEED for receiving random words into registers, resulting in
one function to generate an int and another to generate a long. However,
other architectures don't follow this.

On arm64, the SMCCC TRNG interface can return between one and three
longs. On s390, the CPACF TRNG interface can return arbitrary amounts,
with four longs having the same cost as one. On UML, the os_getrandom()
interface can return arbitrary amounts.

So change the api signature to take a "max_longs" parameter designating
the maximum number of longs requested, and then return the number of
longs generated.

Since callers need to check this return value and loop anyway, each arch
implementation does not bother implementing its own loop to try again to
fill the maximum number of longs. Additionally, all existing callers
pass in a constant max_longs parameter. Taken together, these two things
mean that the codegen doesn't really change much for one-word-at-a-time
platforms, while performance is greatly improved on platforms such as
s390.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/include/linux/random.h b/include/linux/random.h
index 865770e29f3e..3fec206487f6 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -112,19 +112,19 @@ declare_get_random_var_wait(long, unsigned long)
  * 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)
+#ifndef arch_get_random_seed_longs_early
+static inline size_t __init arch_get_random_seed_longs_early(unsigned long *v, size_t max_longs)
 {
 	WARN_ON(system_state != SYSTEM_BOOTING);
-	return arch_get_random_seed_long(v);
+	return arch_get_random_seed_longs(v, max_longs);
 }
 #endif
 
-#ifndef arch_get_random_long_early
-static inline bool __init arch_get_random_long_early(unsigned long *v)
+#ifndef arch_get_random_longs_early
+static inline bool __init arch_get_random_longs_early(unsigned long *v, size_t max_longs)
 {
 	WARN_ON(system_state != SYSTEM_BOOTING);
-	return arch_get_random_long(v);
+	return arch_get_random_longs(v, max_longs);
 }
 #endif