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Date: Wed, 18 Oct 2017 16:17:44 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>, "David S . Miller" <davem@...emloft.net>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, 
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...hat.com>, 
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	Andrey Ryabinin <aryabinin@...tuozzo.com>, Matthias Kaehlcke <mka@...omium.org>, 
	Andy Lutomirski <luto@...nel.org>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, 
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	Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v1 00/27] x86: PIE support and option to extend KASLR randomization

On Thu, Oct 12, 2017 at 9:28 AM, Tom Lendacky <thomas.lendacky@....com> wrote:
> On 10/12/2017 10:34 AM, Thomas Garnier wrote:
>>
>> On Wed, Oct 11, 2017 at 2:34 PM, Tom Lendacky <thomas.lendacky@....com>
>> wrote:
>>>
>>> On 10/11/2017 3:30 PM, Thomas Garnier wrote:
>>>>
>>>> Changes:
>>>>    - patch v1:
>>>>      - Simplify ftrace implementation.
>>>>      - Use gcc mstack-protector-guard-reg=%gs with PIE when possible.
>>>>    - rfc v3:
>>>>      - Use --emit-relocs instead of -pie to reduce dynamic relocation
>>>> space on
>>>>        mapped memory. It also simplifies the relocation process.
>>>>      - Move the start the module section next to the kernel. Remove the
>>>> need for
>>>>        -mcmodel=large on modules. Extends module space from 1 to 2G
>>>> maximum.
>>>>      - Support for XEN PVH as 32-bit relocations can be ignored with
>>>>        --emit-relocs.
>>>>      - Support for GOT relocations previously done automatically with
>>>> -pie.
>>>>      - Remove need for dynamic PLT in modules.
>>>>      - Support dymamic GOT for modules.
>>>>    - rfc v2:
>>>>      - Add support for global stack cookie while compiler default to fs
>>>> without
>>>>        mcmodel=kernel
>>>>      - Change patch 7 to correctly jump out of the identity mapping on
>>>> kexec load
>>>>        preserve.
>>>>
>>>> These patches make the changes necessary to build the kernel as Position
>>>> Independent Executable (PIE) on x86_64. A PIE kernel can be relocated
>>>> below
>>>> the top 2G of the virtual address space. It allows to optionally extend
>>>> the
>>>> KASLR randomization range from 1G to 3G.
>>>
>>>
>>> Hi Thomas,
>>>
>>> I've applied your patches so that I can verify that SME works with PIE.
>>> Unfortunately, I'm running into build warnings and errors when I enable
>>> PIE.
>>>
>>> With CONFIG_STACK_VALIDATION=y I receive lots of messages like this:
>>>
>>>    drivers/scsi/libfc/fc_exch.o: warning: objtool:
>>> fc_destroy_exch_mgr()+0x0: call without frame pointer save/setup
>>>
>>> Disabling CONFIG_STACK_VALIDATION suppresses those.
>>
>>
>> I ran into that, I plan to fix it in the next iteration.
>>
>>>
>>> But near the end of the build, I receive errors like this:
>>>
>>>    arch/x86/kernel/setup.o: In function `dump_kernel_offset':
>>>    .../arch/x86/kernel/setup.c:801:(.text+0x32): relocation truncated to
>>> fit: R_X86_64_32S against symbol `_text' defined in .text section in
>>> .tmp_vmlinux1
>>>    .
>>>    . about 10 more of the above type messages
>>>    .
>>>    make: *** [vmlinux] Error 1
>>>    Error building kernel, exiting
>>>
>>> Are there any config options that should or should not be enabled when
>>> building with PIE enabled?  Is there a compiler requirement for PIE (I'm
>>> using gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.5))?
>>
>>
>> I never ran into these ones and I tested compilers older and newer.
>> What was your exact configuration?
>
>
> I'll send you the config in a separate email.
>
> Thanks,
> Tom

Thanks for your feedback (Tom and Markus). The issue was linked to
using a modern gcc with a modern linker, I managed to repro and fix it
on my current version.

I will create a v1.5 for Kees Cook to keep on one of his branch for
few weeks so I can collect as much feedback from 0day. After that I
will send v2.

>
>
>>
>>>
>>> Thanks,
>>> Tom
>>>
>>>>
>>>> Thanks a lot to Ard Biesheuvel & Kees Cook on their feedback on compiler
>>>> changes, PIE support and KASLR in general. Thanks to Roland McGrath on
>>>> his
>>>> feedback for using -pie versus --emit-relocs and details on compiler
>>>> code
>>>> generation.
>>>>
>>>> The patches:
>>>>    - 1-3, 5-1#, 17-18: Change in assembly code to be PIE compliant.
>>>>    - 4: Add a new _ASM_GET_PTR macro to fetch a symbol address
>>>> generically.
>>>>    - 14: Adapt percpu design to work correctly when PIE is enabled.
>>>>    - 15: Provide an option to default visibility to hidden except for
>>>> key symbols.
>>>>          It removes errors between compilation units.
>>>>    - 16: Adapt relocation tool to handle PIE binary correctly.
>>>>    - 19: Add support for global cookie.
>>>>    - 20: Support ftrace with PIE (used on Ubuntu config).
>>>>    - 21: Fix incorrect address marker on dump_pagetables.
>>>>    - 22: Add option to move the module section just after the kernel.
>>>>    - 23: Adapt module loading to support PIE with dynamic GOT.
>>>>    - 24: Make the GOT read-only.
>>>>    - 25: Add the CONFIG_X86_PIE option (off by default).
>>>>    - 26: Adapt relocation tool to generate a 64-bit relocation table.
>>>>    - 27: Add the CONFIG_RANDOMIZE_BASE_LARGE option to increase
>>>> relocation range
>>>>          from 1G to 3G (off by default).
>>>>
>>>> Performance/Size impact:
>>>>
>>>> Size of vmlinux (Default configuration):
>>>>    File size:
>>>>    - PIE disabled: +0.000031%
>>>>    - PIE enabled: -3.210% (less relocations)
>>>>    .text section:
>>>>    - PIE disabled: +0.000644%
>>>>    - PIE enabled: +0.837%
>>>>
>>>> Size of vmlinux (Ubuntu configuration):
>>>>    File size:
>>>>    - PIE disabled: -0.201%
>>>>    - PIE enabled: -0.082%
>>>>    .text section:
>>>>    - PIE disabled: same
>>>>    - PIE enabled: +1.319%
>>>>
>>>> Size of vmlinux (Default configuration + ORC):
>>>>    File size:
>>>>    - PIE enabled: -3.167%
>>>>    .text section:
>>>>    - PIE enabled: +0.814%
>>>>
>>>> Size of vmlinux (Ubuntu configuration + ORC):
>>>>    File size:
>>>>    - PIE enabled: -3.167%
>>>>    .text section:
>>>>    - PIE enabled: +1.26%
>>>>
>>>> The size increase is mainly due to not having access to the 32-bit
>>>> signed
>>>> relocation that can be used with mcmodel=kernel. A small part is due to
>>>> reduced
>>>> optimization for PIE code. This bug [1] was opened with gcc to provide a
>>>> better
>>>> code generation for kernel PIE.
>>>>
>>>> Hackbench (50% and 1600% on thread/process for pipe/sockets):
>>>>    - PIE disabled: no significant change (avg +0.1% on latest test).
>>>>    - PIE enabled: between -0.50% to +0.86% in average (default and
>>>> Ubuntu config).
>>>>
>>>> slab_test (average of 10 runs):
>>>>    - PIE disabled: no significant change (-2% on latest run, likely
>>>> noise).
>>>>    - PIE enabled: between -1% and +0.8% on latest runs.
>>>>
>>>> Kernbench (average of 10 Half and Optimal runs):
>>>>    Elapsed Time:
>>>>    - PIE disabled: no significant change (avg -0.239%)
>>>>    - PIE enabled: average +0.07%
>>>>    System Time:
>>>>    - PIE disabled: no significant change (avg -0.277%)
>>>>    - PIE enabled: average +0.7%
>>>>
>>>> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82303
>>>>
>>>> diffstat:
>>>>    Documentation/x86/x86_64/mm.txt              |    3
>>>>    arch/x86/Kconfig                             |   43 ++++++
>>>>    arch/x86/Makefile                            |   40 +++++
>>>>    arch/x86/boot/boot.h                         |    2
>>>>    arch/x86/boot/compressed/Makefile            |    5
>>>>    arch/x86/boot/compressed/misc.c              |   10 +
>>>>    arch/x86/crypto/aes-x86_64-asm_64.S          |   45 ++++--
>>>>    arch/x86/crypto/aesni-intel_asm.S            |   14 +-
>>>>    arch/x86/crypto/aesni-intel_avx-x86_64.S     |    6
>>>>    arch/x86/crypto/camellia-aesni-avx-asm_64.S  |   42 +++---
>>>>    arch/x86/crypto/camellia-aesni-avx2-asm_64.S |   44 +++---
>>>>    arch/x86/crypto/camellia-x86_64-asm_64.S     |    8 -
>>>>    arch/x86/crypto/cast5-avx-x86_64-asm_64.S    |   50 ++++---
>>>>    arch/x86/crypto/cast6-avx-x86_64-asm_64.S    |   44 +++---
>>>>    arch/x86/crypto/des3_ede-asm_64.S            |   96 +++++++++-----
>>>>    arch/x86/crypto/ghash-clmulni-intel_asm.S    |    4
>>>>    arch/x86/crypto/glue_helper-asm-avx.S        |    4
>>>>    arch/x86/crypto/glue_helper-asm-avx2.S       |    6
>>>>    arch/x86/entry/entry_32.S                    |    3
>>>>    arch/x86/entry/entry_64.S                    |   29 ++--
>>>>    arch/x86/include/asm/asm.h                   |   13 +
>>>>    arch/x86/include/asm/bug.h                   |    2
>>>>    arch/x86/include/asm/ftrace.h                |    6
>>>>    arch/x86/include/asm/jump_label.h            |    8 -
>>>>    arch/x86/include/asm/kvm_host.h              |    6
>>>>    arch/x86/include/asm/module.h                |   11 +
>>>>    arch/x86/include/asm/page_64_types.h         |    9 +
>>>>    arch/x86/include/asm/paravirt_types.h        |   12 +
>>>>    arch/x86/include/asm/percpu.h                |   25 ++-
>>>>    arch/x86/include/asm/pgtable_64_types.h      |    6
>>>>    arch/x86/include/asm/pm-trace.h              |    2
>>>>    arch/x86/include/asm/processor.h             |   12 +
>>>>    arch/x86/include/asm/sections.h              |    8 +
>>>>    arch/x86/include/asm/setup.h                 |    2
>>>>    arch/x86/include/asm/stackprotector.h        |   19 ++
>>>>    arch/x86/kernel/acpi/wakeup_64.S             |   31 ++--
>>>>    arch/x86/kernel/asm-offsets.c                |    3
>>>>    arch/x86/kernel/asm-offsets_32.c             |    3
>>>>    arch/x86/kernel/asm-offsets_64.c             |    3
>>>>    arch/x86/kernel/cpu/common.c                 |    7 -
>>>>    arch/x86/kernel/cpu/microcode/core.c         |    4
>>>>    arch/x86/kernel/ftrace.c                     |   42 +++++-
>>>>    arch/x86/kernel/head64.c                     |   32 +++-
>>>>    arch/x86/kernel/head_32.S                    |    3
>>>>    arch/x86/kernel/head_64.S                    |   41 +++++-
>>>>    arch/x86/kernel/kvm.c                        |    6
>>>>    arch/x86/kernel/module.c                     |  182
>>>> ++++++++++++++++++++++++++-
>>>>    arch/x86/kernel/module.lds                   |    3
>>>>    arch/x86/kernel/process.c                    |    5
>>>>    arch/x86/kernel/relocate_kernel_64.S         |    8 -
>>>>    arch/x86/kernel/setup_percpu.c               |    2
>>>>    arch/x86/kernel/vmlinux.lds.S                |   13 +
>>>>    arch/x86/kvm/svm.c                           |    4
>>>>    arch/x86/lib/cmpxchg16b_emu.S                |    8 -
>>>>    arch/x86/mm/dump_pagetables.c                |   11 +
>>>>    arch/x86/power/hibernate_asm_64.S            |    4
>>>>    arch/x86/tools/relocs.c                      |  170
>>>> +++++++++++++++++++++++--
>>>>    arch/x86/tools/relocs.h                      |    4
>>>>    arch/x86/tools/relocs_common.c               |   15 +-
>>>>    arch/x86/xen/xen-asm.S                       |   12 -
>>>>    arch/x86/xen/xen-head.S                      |    9 -
>>>>    arch/x86/xen/xen-pvh.S                       |   13 +
>>>>    drivers/base/firmware_class.c                |    4
>>>>    include/asm-generic/sections.h               |    6
>>>>    include/asm-generic/vmlinux.lds.h            |   12 +
>>>>    include/linux/compiler.h                     |    8 +
>>>>    init/Kconfig                                 |    9 +
>>>>    kernel/kallsyms.c                            |   16 +-
>>>>    kernel/trace/trace.h                         |    4
>>>>    lib/dynamic_debug.c                          |    4
>>>>    70 files changed, 1032 insertions(+), 308 deletions(-)
>>>>
>>
>>
>>
>



-- 
Thomas

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