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, 7 insertions, 22 deletions

diff --git a/arch/s390/include/asm/archrandom.h b/arch/s390/include/asm/archrandom.h
index 0a1c2e66c709..cf5e000df0a1 100644
--- a/arch/s390/include/asm/archrandom.h
+++ b/arch/s390/include/asm/archrandom.h
@@ -18,34 +18,19 @@
 DECLARE_STATIC_KEY_FALSE(s390_arch_random_available);
 extern atomic64_t s390_arch_random_counter;
 
-static inline bool __must_check arch_get_random_long(unsigned long *v)
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
 {
-	return false;
+	return 0;
 }
 
-static inline bool __must_check arch_get_random_int(unsigned int *v)
-{
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
-{
-	if (static_branch_likely(&s390_arch_random_available)) {
-		cpacf_trng(NULL, 0, (u8 *)v, sizeof(*v));
-		atomic64_add(sizeof(*v), &s390_arch_random_counter);
-		return true;
-	}
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
 {
 	if (static_branch_likely(&s390_arch_random_available)) {
-		cpacf_trng(NULL, 0, (u8 *)v, sizeof(*v));
-		atomic64_add(sizeof(*v), &s390_arch_random_counter);
-		return true;
+		cpacf_trng(NULL, 0, (u8 *)v, max_longs * sizeof(*v));
+		atomic64_add(max_longs * sizeof(*v), &s390_arch_random_counter);
+		return max_longs;
 	}
-	return false;
+	return 0;
 }
 
 #endif /* _ASM_S390_ARCHRANDOM_H */