linux-kernel - Re: [PATCH] aarch64: vdso: Wire up getrandom() vDSO implementation

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Message-ID: <ZszlGPqfrULzi3KG@zx2c4.com>
Date: Mon, 26 Aug 2024 22:27:04 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Adhemerval Zanella <adhemerval.zanella@...aro.org>
Cc: Theodore Ts'o <tytso@....edu>, linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-arch@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Eric Biggers <ebiggers@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH] aarch64: vdso: Wire up getrandom() vDSO implementation

Hi Adhemerval,

Thanks for posting this! Exciting to have it here.

Just some small nits for now:

On Mon, Aug 26, 2024 at 06:10:40PM +0000, Adhemerval Zanella wrote:
> +static __always_inline ssize_t getrandom_syscall(void *buffer, size_t len, unsigned int flags)
> +{
> +	register long int x8 asm ("x8") = __NR_getrandom;
> +	register long int x0 asm ("x0") = (long int) buffer;
> +	register long int x1 asm ("x1") = (long int) len;
> +	register long int x2 asm ("x2") = (long int) flags;

Usually it's written just as `long` or `unsigned long`, and likewise
with the cast. Also, no space after the cast.

> +#define __VDSO_RND_DATA_OFFSET  480

This is the size of the data currently there?

>  #include <asm/page.h>
>  #include <asm/vdso.h>
>  #include <asm-generic/vmlinux.lds.h>
> +#include <vdso/datapage.h>
> +#include <asm/vdso/vsyscall.h>

Possible to keep the asm/ together?

> + * ARM64 ChaCha20 implementation meant for vDSO.  Produces a given positive
> + * number of blocks of output with nonnce 0, taking an input key and 8-bytes

nonnce -> nonce

> -ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/x86/ -e s/x86_64/x86/)
> +ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/x86/ -e s/x86_64/x86/ -e s/aarch64.*/arm64/)
>  SODIUM := $(shell pkg-config --libs libsodium 2>/dev/null)
>  
>  TEST_GEN_PROGS := vdso_test_gettimeofday
> @@ -11,7 +11,7 @@ ifeq ($(ARCH),$(filter $(ARCH),x86 x86_64))
>  TEST_GEN_PROGS += vdso_standalone_test_x86
>  endif
>  TEST_GEN_PROGS += vdso_test_correctness
> -ifeq ($(uname_M),x86_64)
> +ifeq ($(uname_M), $(filter x86_64 aarch64, $(uname_M)))
>  TEST_GEN_PROGS += vdso_test_getrandom
>  ifneq ($(SODIUM),)
>  TEST_GEN_PROGS += vdso_test_chacha

You'll need to add the symlink to get the chacha selftest running:

  $ ln -s ../../../arch/arm64/kernel/vdso tools/arch/arm64/vdso
  $ git add tools/arch/arm64/vdso

Also, can you confirm that the chacha selftest runs and works?

Jason