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

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Message-ID: <877cwltmno.ffs@tglx>
Date:   Mon, 13 Feb 2023 20:01:31 +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: [PING][PATCH v3] x86: Use `get_random_u8' for kernel stack
 offset randomization

On Sun, Feb 12 2023 at 23:17, Maciej W. Rozycki wrote:
> On Mon, 30 Jan 2023, Maciej W. Rozycki wrote:
>
>> For x86 kernel stack offset randomization uses the RDTSC instruction, 
>> which according to H. Peter Anvin is not a secure source of entropy:
>> 
>> "RDTSC isn't a super fast instruction either, but what is *way* more
>> significant is that this use of RDTSC is NOT safe: in certain power states
>> it may very well be that stone number of lower bits of TSC contain no
>> entropy at all."
>
>  Ping for:
> <https://lore.kernel.org/all/alpine.DEB.2.21.2301302011150.55843@angie.orcam.me.uk/>.

I'm waiting for you to address Peter Anvins feedback. You also cite him
w/o providing a link to the conversation, so any context is missing.

Thanks,

        tglx