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

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

On 10/12/2017 10:34 AM, Thomas Garnier wrote:
> On Wed, Oct 11, 2017 at 2:34 PM, Tom Lendacky <thomas.lendacky@xxxxxxx> 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,
> > 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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