Re: [PATCH v4 1/4] LoongArch: vDSO: Wire up getrandom() vDSO implementation

["Jason A. Donenfeld" <Jason@zx2c4.com>]

On Tue, Aug 27, 2024 at 09:20:14PM +0800, Xi Ruoyao wrote:
> diff --git a/arch/loongarch/vdso/vgetrandom-chacha.S b/arch/loongarch/vdso/vgetrandom-chacha.S
> new file mode 100644
> index 000000000000..2e42198f2faf
> --- /dev/null
> +++ b/arch/loongarch/vdso/vgetrandom-chacha.S
> @@ -0,0 +1,239 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 Xi Ruoyao <xry111@xry111.site>. All Rights Reserved.
> + */
> +
> +#include <asm/asm.h>
> +#include <asm/regdef.h>
> +#include <linux/linkage.h>
> +
> +.text
> +
> +/* Salsa20 quarter-round */
> +.macro	QR	a b c d
> +	add.w		\a, \a, \b
> +	xor		\d, \d, \a
> +	rotri.w		\d, \d, 16
> +
> +	add.w		\c, \c, \d
> +	xor		\b, \b, \c
> +	rotri.w		\b, \b, 20
> +
> +	add.w		\a, \a, \b
> +	xor		\d, \d, \a
> +	rotri.w		\d, \d, 24
> +
> +	add.w		\c, \c, \d
> +	xor		\b, \b, \c
> +	rotri.w		\b, \b, 25
> +.endm
> +
> +/*
> + * Very basic LoongArch implementation of ChaCha20. Produces a given positive
> + * number of blocks of output with a nonce of 0, taking an input key and
> + * 8-byte counter. Importantly does not spill to the stack. Its arguments
> + * are:
> + *
> + *	a0: output bytes
> + *	a1: 32-byte key input
> + *	a2: 8-byte counter input/output
> + *	a3: number of 64-byte blocks to write to output
> + */
> +SYM_FUNC_START(__arch_chacha20_blocks_nostack)

I can confirm this works:

    $ loongarch64-unknown-linux-gnu-gcc -std=gnu99 -D_GNU_SOURCE= -idirafter tools/testing/selftests/../../../tools/include -idirafter tools/testing/selftests/../../../arch/loongarch/include -idirafter tools/testing/selftests/../../../include -D__ASSEMBLY__ -Wa,--noexecstack    vdso_test_chacha.c tools/testing/selftests/../../../tools/arch/loongarch/vdso/vgetrandom-chacha.S  -o tools/testing/selftests/vDSO/vdso_test_chacha -static
    $ qemu-loongarch64 ./vdso_test_chacha
    TAP version 13
    1..1
    ok 1 chacha: PASS
    
Just waiting now on a v5 as discussed and acks from the LoongArch maintainers on that v5.

Jason