linux-kernel - Re: [PATCH v4 2/3] random: introduce generic vDSO getrandom() implementation

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Date:   Sat, 19 Nov 2022 01:04:35 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>,
        Carlos O'Donell <carlos@...hat.com>
Subject: Re: [PATCH v4 2/3] random: introduce generic vDSO getrandom()
 implementation

On Sat, Nov 19, 2022 at 12:55:02AM +0100, Jason A. Donenfeld wrote:
> Sorry if I'm a bit slow here to grok what's up.

Okay, I think I see it now. That's a complicated patch for a simple idea
because gettime is more complicated than getrandom. I suspect what you
want is something like the below, correct? Seems easy enough.

diff --git a/lib/vdso/getrandom.c b/lib/vdso/getrandom.c
index b253e9247706..b3282d7cfb53 100644
--- a/lib/vdso/getrandom.c
+++ b/lib/vdso/getrandom.c
@@ -41,10 +41,10 @@ static void memcpy_and_zero(void *dst, void *src, size_t len)
 }

 static __always_inline ssize_t
-__cvdso_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state)
+__cvdso_getrandom_data(const struct vdso_rng_data *rng_info, void *buffer, size_t len,
+		       unsigned int flags, void *opaque_state)
 {
 	struct vgetrandom_state *state = opaque_state;
-	const struct vdso_rng_data *rng_info = __arch_get_vdso_rng_data();
 	u32 chacha_state[CHACHA_STATE_WORDS];
 	ssize_t ret = min_t(size_t, MAX_RW_COUNT, len);
 	unsigned long current_generation;
@@ -107,3 +107,9 @@ __cvdso_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_sta
 	memzero_explicit(chacha_state, sizeof(chacha_state));
 	goto more_batch;
 }
+
+static __always_inline ssize_t
+__cvdso_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state)
+{
+	return __cvdso_getrandom_data(__arch_get_vdso_rng_data(), buffer, len, flags, opaque_state);
+}