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

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Message-ID: <2236FBA76BA1254E88B949DDB74E612BA4C61E91@IRSMSX102.ger.corp.intel.com>
Date:   Thu, 25 Apr 2019 11:23:57 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     David Laight <David.Laight@...LAB.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?

Do you have any pointers on this? I did an online search, but could not find anything
concrete. The Intel manual doesn't talk about precision at all, only about protected
mode.

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

You mean additional constructions on top of TSC is pointless? 

Best Regards,
Elena.