random: handle archrandom with multiple longs
authorJason A. Donenfeld <Jason@zx2c4.com>
Sun, 17 Jul 2022 10:35:24 +0000 (12:35 +0200)
committerJason A. Donenfeld <Jason@zx2c4.com>
Mon, 25 Jul 2022 11:26:14 +0000 (13:26 +0200)
commitd349ab99eec7ab0f977fc4aac27aa476907acf90
treeb98736b45c4f0c00ea2e00e5cefe543bd2ce0759
parent0b9ba6135d7f18b82f3d8bebb55ded725ba88e0e
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>
arch/arm64/include/asm/archrandom.h
arch/arm64/kernel/kaslr.c
arch/powerpc/include/asm/archrandom.h
arch/powerpc/kvm/book3s_hv.c
arch/s390/include/asm/archrandom.h
arch/um/include/asm/archrandom.h
arch/x86/include/asm/archrandom.h
arch/x86/kernel/espfix_64.c
drivers/char/random.c
include/asm-generic/archrandom.h
include/linux/random.h