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Date: Thu, 12 Oct 2017 08:34:13 -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>,
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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 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?
>
> 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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