Date: Mon, 8 Apr 2019 08:58:54 -0700 From: Thomas Garnier <thgarnie@...omium.org> To: Christopher Lameter <cl@...ux.com> 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 Fri, Feb 1, 2019 at 9:13 AM Thomas Garnier <thgarnie@...omium.org> wrote: > > On Thu, Jan 31, 2019 at 6:31 PM Christopher Lameter <cl@...ux.com> wrote: > > > > On Thu, 31 Jan 2019, Thomas Garnier wrote: > > > > > The per-cpu symbols are in a section that is zero based to create > > > offsets. The compiler doesn't see them as offsets but as relative > > > symbol and try to relocate them. Given the distance between zero and > > > the mapped kernel is much larger than the instruction offset range, it > > > fails to do it. > > > > We switch that off in the linker. If that does not work with your > > modifications then you need to figure out how to update the link > > configuration. > > > > 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. Christopher: Did you have something specific in mind? I checked the following: - Changing the FLAGS() on the PHDRS. - using -z noreloc-overflow which actually doesn't seem to apply to PC32 relocations. - Look at all linker options and script format for anything around that.
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