linux-kernel - Re: [PATCH v6 14/27] x86/percpu: Adapt percpu for PIE support

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Date:   Mon, 8 Apr 2019 17:56:20 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Thomas Garnier <thgarnie@...omium.org>
cc:     Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joerg Roedel <jroedel@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        LKML <linux-kernel@...r.kernel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH v6 14/27] x86/percpu: Adapt percpu for PIE support

On Mon, 8 Apr 2019, Thomas Garnier wrote:

> > It didn't work originally but I will revisit to see if I missed something.
>
> I revisited and couldn't find a way to prevent relocations to the
> percpu section. Without PIE, you can reference absolute address which
> was convenient for percpu.

Can you switch PIE off for the percpu section? If not maybe the linker
needs to have an additional option?

Cannot imagine that this is not possible. You neeed to be able to
reference registers that are in fixed memory locations.


> Christopher: Did you have something specific in mind?

I thought that we just leave it as is.