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

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Message-ID: <CAHk-=wjb9c4JV5xOWp5VMGTzgCmpFCegf2MydVwbvjr5gnBV9A@mail.gmail.com>
Date:   Fri, 3 May 2019 12:10:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     "Reshetova, Elena" <elena.reshetova@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Eric Biggers <ebiggers3@...il.com>,
        "ebiggers@...gle.com" <ebiggers@...gle.com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        Peter Zijlstra <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        Daniel Borkmann <daniel@...earbox.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>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

On Fri, May 3, 2019 at 9:40 AM David Laight <David.Laight@...lab.com> wrote:
>
> That gives you 10 system calls per rdrand instruction
> and mostly takes the latency out of line.

Do we really want to do this? What is the attack scenario?

With no VLA's, and the stackleak plugin, what's the upside? Are we
adding random code (literally) "just because"?

                   Linus