Re: [PATCH v3] random: handle archrandom with multiple longs

Borislav Petkov
2022-07-25T11:25:43Z

On Tue, Jul 19, 2022 at 03:02:07PM +0200, Jason A. Donenfeld wrote:
> 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 1 and 3 longs. On
> s390, the CPACF TRNG interface can return arbitrary amounts, with 32
> 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.
>
> Cc: Will Deacon <will@kernel.org>
> Cc: Alexander Gordeev <agordeev@linux.ibm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Heiko Carstens <hca@linux.ibm.com>
> Cc: Johannes Berg <johannes@sipsolutions.net>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Harald Freudenberger <freude@linux.ibm.com>
> Acked-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
> arch/arm64/include/asm/archrandom.h | 102 ++++++++++++--------------
> arch/arm64/kernel/kaslr.c | 2 +-
> arch/powerpc/include/asm/archrandom.h | 30 ++------
> arch/powerpc/kvm/book3s_hv.c | 2 +-
> arch/s390/include/asm/archrandom.h | 29 ++------
> arch/um/include/asm/archrandom.h | 21 ++----
> arch/x86/include/asm/archrandom.h | 41 +----------
> arch/x86/kernel/espfix_64.c | 2 +-
> drivers/char/random.c | 45 ++++++++----
> include/asm-generic/archrandom.h | 18 +----
> include/linux/random.h | 12 +--
> 11 files changed, 116 insertions(+), 188 deletions(-)

Acked-by: Borislav Petkov <bp@suse.de> # for x86

Thx.

--
Regards/Gruss,
Boris.

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