linux-kernel - Re: early x86 unseeded randomness

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Message-ID: <20170815134514.r6qjotjgfmurwh64@pd.tnic>
Date:   Tue, 15 Aug 2017 15:45:14 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...nel.org>, Willy Tarreau <w@....eu>,
        Theodore Ts'o <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        x86-ml <x86@...nel.org>, "Jason A. Donenfeld" <Jason@...c4.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nicholas Mc Guire <der.herr@...r.at>
Subject: Re: early x86 unseeded randomness

On Tue, Aug 15, 2017 at 12:47:36PM +0200, Thomas Gleixner wrote:
> 8<-------------------
> 
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -1360,3 +1360,19 @@ unsigned long calibrate_delay_is_known(v
>  	return 0;
>  }
>  #endif
> +
> +u64 __init tsc_early_random(void)
> +{
> +	u64 uninitialized_var(res);
> +	int i;
> +
> +	if (!boot_cpu_has(X86_FEATURE_TSC))
> +		return res;
> +
> +	res ^= rdtsc();
> +	for (i = 0; i < BITS_PER_LONG; i++) {
> +		res ^= ((rdtsc() & 0x04) >> 2) << i;
> +		udelay(2);
> +	}
> +	return res;
> +}

Something like this is exactly what I was aiming at with my dumb patch.
We could use this for early boot randomness on x86.

Should I turn it into proper patches or you want to?

-- 
Regards/Gruss,
    Boris.

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