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From: Thomas Garnier <thgarnie@chromium.org>
To: Christopher Lameter <cl@linux.com>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>,
	kristen@linux.intel.com, Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andi Kleen <ak@linux.intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Michal Hocko <mhocko@suse.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Cao jin <caoj.fnst@cn.fujitsu.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Joerg Roedel <jroedel@suse.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Kees Cook <keescook@chromium.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	LKML <linux-kernel@vger.kernel.org>,
	xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v6 14/27] x86/percpu: Adapt percpu for PIE support
Date: Thu, 31 Jan 2019 14:49:04 -0800	[thread overview]
Message-ID: <CAJcbSZGKR7dKVqNEDEO7Qzf7tnNqmL=p1uVKvsUefS=Hs-=iNA@mail.gmail.com> (raw)
In-Reply-To: <01000168a5b35a86-b79bfe67-191e-43bc-a5c7-0e74eac06195-000000@email.amazonses.com>

On Thu, Jan 31, 2019 at 12:57 PM Christopher Lameter <cl@linux.com> wrote:
>
> On Thu, 31 Jan 2019, Thomas Garnier wrote:
>
> > Perpcu uses a clever design where the .percu ELF section has a virtual
> > address of zero and the custom linux relocation code avoid relocating
> > specific symbols. It makes the code simple and easily adaptable with or
> > without SMP support.
>
> We usually talk about this as offsets rather than addressess. The intend
> here is to give every processor its own address that is unique for this
> processor. Operations are always relative to a segment register and the
> whole area can be relocated at will by simply changing the segment
> register.
>
> > This design is incompatible with PIE. While creating a PIE binary, the
> > copmiler tries to make everything relative. The compiler will attempt to
>
> This is very compatible with PIE because it is already relative.

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.

>
> > generate instructions with the distance between zero and any 64-bit
> > virtual address. It will fail as the relocation range cannot fit within
> > the possible instructions accessing a segment register.
>
> Leave the offsets alone and just change the segment register if you need
> to relocate the area of a specific processor?
>
> > The assembly and PER_CPU macros are changed to use relative references
> > when PIE is enabled.
>
> They already use relative reference. What is the point here?
>
> > --- a/arch/x86/include/asm/percpu.h
> > +++ b/arch/x86/include/asm/percpu.h
> > @@ -5,9 +5,11 @@
> >  #ifdef CONFIG_X86_64
> >  #define __percpu_seg         gs
> >  #define __percpu_mov_op              movq
> > +#define __percpu_rel         (%rip)
>
> The percpu section cannot be IP relative since we need to have separate
> address spaces per cpu.
>

  reply	other threads:[~2019-01-31 22:49 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-31 19:24 [PATCH v6 00/27] x86: PIE support and option to extend KASLR randomization Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 01/27] x86/crypto: Adapt assembly for PIE support Thomas Garnier
2019-02-07 11:48   ` Borislav Petkov
2019-02-07 17:01     ` Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 02/27] x86: Use symbol name in jump table " Thomas Garnier
2019-02-07 12:17   ` Borislav Petkov
2019-02-07 17:04     ` Thomas Garnier
2019-02-07 17:11       ` Borislav Petkov
2019-02-07 23:55         ` Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 03/27] x86: Add macro to get symbol address " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 04/27] x86: relocate_kernel - Adapt assembly " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 05/27] x86/entry/64: " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 06/27] x86: pm-trace - " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 07/27] x86/CPU: " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 08/27] x86/acpi: " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 09/27] x86/boot/64: " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 10/27] x86/power/64: " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 11/27] x86/paravirt: " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 12/27] x86/alternatives: " Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 13/27] x86/boot/64: Build head64.c as mcmodel large when PIE is enabled Thomas Garnier
2019-02-01 11:15   ` Kirill A. Shutemov
2019-02-01 17:11     ` Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 14/27] x86/percpu: Adapt percpu for PIE support Thomas Garnier
2019-01-31 20:57   ` Christopher Lameter
2019-01-31 22:49     ` Thomas Garnier [this message]
2019-02-01  2:31       ` Christopher Lameter
2019-02-01 17:13         ` Thomas Garnier
2019-04-08 15:58           ` Thomas Garnier
2019-04-08 17:56             ` Christopher Lameter
2019-04-08 18:08               ` Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 15/27] compiler: Option to default to hidden symbols Thomas Garnier
2019-02-01  7:12   ` Dan Carpenter
2019-02-01 17:00     ` Thomas Garnier
2019-02-01  8:22   ` Adrian Hunter
2019-02-01 17:35     ` Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 16/27] compiler: Option to add PROVIDE_HIDDEN replacement for weak symbols Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 17/27] x86/relocs: Handle PIE relocations Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 18/27] xen: Adapt assembly for PIE support Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 19/27] kvm: " Thomas Garnier
2019-02-06 19:56   ` Sean Christopherson
2019-02-06 21:23     ` Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 20/27] x86: Support global stack cookie Thomas Garnier
2019-02-01 19:27   ` Andy Lutomirski
2019-02-01 20:21     ` Thomas Garnier
2019-02-01 22:36       ` Andy Lutomirski
2019-02-01 23:56         ` Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 21/27] x86/ftrace: Adapt function tracing for PIE support Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 22/27] x86/modules: Add option to start module section after kernel Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 23/27] x86/modules: Adapt module loading for PIE support Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 24/27] x86/mm: Make the x86 GOT read-only Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 25/27] x86/pie: Add option to build the kernel as PIE Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 26/27] x86/relocs: Add option to generate 64-bit relocations Thomas Garnier
2019-01-31 19:24 ` [PATCH v6 27/27] x86/kaslr: Add option to extend KASLR range from 1GB to 3GB Thomas Garnier
2019-01-31 19:59 ` [PATCH v6 00/27] x86: PIE support and option to extend KASLR randomization Kees Cook
2019-01-31 21:40 ` Konrad Rzeszutek Wilk
2019-01-31 22:42   ` Thomas Garnier

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