linux-kernel - RE: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

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Date:   Wed, 24 Apr 2019 13:33:08 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Reshetova, Elena'" <elena.reshetova@...el.com>,
        'Theodore Ts'o' <tytso@....edu>,
        Ingo Molnar <mingo@...nel.org>,
        'Peter Zijlstra' <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        "luto@...nel.org" <luto@...nel.org>,
        "luto@...capital.net" <luto@...capital.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "Perla, Enrico" <enrico.perla@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: RE: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

From: Reshetova, Elena
> Sent: 24 April 2019 12:43
>
> Sorry for the delay - Easter holidays + I was trying to arrange my brain around proposed options.
> Here what I think our options are with regards to the source of randomness:
> 
> 1) rdtsc or variations based on it (David proposed some CRC-based variants for example)

Do I remember something about rdtsc being made less accurate in order to
make it (slightly) more difficult to use it to measure timing attacks?

If true, and it applies to the kernel (eg in a VM) then this is probably
all pointless!

	David

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