linux-kernel - Re: [PATCH 1/1] x86/entry/64: randomize kernel stack offset upon syscall

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Message-ID: <CAGXu5j+iPwqp6ReGh6FEGNWtsv3AT73XgJzVOoMinemSZNfUaQ@mail.gmail.com>
Date:   Wed, 10 Apr 2019 09:20:46 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Elena Reshetova <elena.reshetova@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        "Perla, Enrico" <enrico.perla@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/1] x86/entry/64: randomize kernel stack offset upon syscall

On Wed, Apr 10, 2019 at 7:49 AM Andy Lutomirski <luto@...nel.org> wrote:
> And build it like this, it fails:
>
> $ gcc -o ingo -g ingo.c -pie
> /usr/bin/ld: /tmp/ccofYU9N.o: relocation R_X86_64_32 against `.rodata'
> can not be used when making a PIE object; recompile with -fPIC
> /usr/bin/ld: final link failed: nonrepresentable section on output
> collect2: error: ld returned 1 exit status
>
> Which I assume means that -pie requires -fPIC, and your toolchain is
> screwed up and is defaulting to useless options.  I'm guessing you
> should file a bug against your distro gcc package.  For me, it works
> if I remove -pie.

I think you need both -fPIE (object creation) and -pie (linking).

-- 
Kees Cook