From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Maciej W. Rozycki" <macro@orcam.me.uk>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Kees Cook <keescook@chromium.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PING][PATCH v3] x86: Use `get_random_u8' for kernel stack
 offset randomization
In-Reply-To: <alpine.DEB.2.21.2302122311470.46819@angie.orcam.me.uk>
References: <alpine.DEB.2.21.2301302011150.55843@angie.orcam.me.uk>
 <alpine.DEB.2.21.2302122311470.46819@angie.orcam.me.uk>
Date:   Mon, 13 Feb 2023 20:01:31 +0100
Message-ID: <877cwltmno.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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