linux-kernel - Re: [PATCH v3] x86: Use `get_random_u8' for kernel stack offset randomization

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Message-ID: <874jrptmk9.ffs@tglx>
Date:   Mon, 13 Feb 2023 20:03:34 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Kees Cook <keescook@...omium.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] x86: Use `get_random_u8' for kernel stack offset
 randomization

On Mon, Jan 30 2023 at 21:30, Maciej W. Rozycki wrote:
>
> Therefore switch to our generic entropy source and use `get_random_u8' 
> instead, which according to Jason A. Donenfeld is supposed to be fast 
> enough:
>
> "Generally it's very very fast, as most cases wind up being only a
> memcpy -- in this case, a single byte copy. So by and large it should
> be suitable. It's fast enough now that most networking things are able
> to use it. And lots of other places where you'd want really high
> performance. So I'd expect it's okay to use here too. And if it is too
> slow, we should figure out how to make it faster. But I don't suspect
> it'll be too slow."

Please provide numbers on contemporary hardware.

Up to that point, it's easy enough to just disable that randomization on
32bit.

Thanks,

        tglx