Re: [Xen-devel] [PATCH v1 00/27] x86: PIE support and option to extend KASLR randomization

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

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.

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))?

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(-)
> 

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