Re: [PATCH v11 00/11] x86: PIE support to extend KASLR randomization

[Kees Cook <keescook@chromium.org>]

On Thu, Feb 27, 2020 at 04:00:45PM -0800, Thomas Garnier wrote:
> Minor changes based on feedback and rebase from v10.
> 
> Splitting the previous serie in two. This part contains assembly code
> changes required for PIE but without any direct dependencies with the
> rest of the patchset.
> 
> Note: Using objtool to detect non-compliant PIE relocations is not yet
> possible as this patchset only includes the simplest PIE changes.
> Additional changes are needed in kvm, xen and percpu code.
> 
> Changes:
>  - patch v11 (assembly);
>    - Fix comments on x86/entry/64.
>    - Remove KASLR PIE explanation on all commits.
>    - Add note on objtool not being possible at this stage of the patchset.

This moves us closer to PIE in a clean first step. I think these patches
look good to go, and unblock the work in kvm, xen, and percpu code. Can
one of the x86 maintainers pick this series up?

Thanks!

-Kees

>  - patch v10 (assembly):
>    - Swap rax for rdx on entry/64 changes based on feedback.
>    - Addressed feedback from Borislav Petkov on boot, paravirt, alternatives
>      and globally.
>    - Rebased the patchset and ensure it works with large kaslr (not included).
>  - patch v9 (assembly):
>    - Moved to relative reference for sync_core based on feedback.
>    - x86/crypto had multiple algorithms deleted, removed PIE changes to them.
>    - fix typo on comment end line.
>  - patch v8 (assembly):
>    - Fix issues in crypto changes (thanks to Eric Biggers).
>    - Remove unnecessary jump table change.
>    - Change author and signoff to chromium email address.
>  - patch v7 (assembly):
>    - Split patchset and reorder changes.
>  - patch v6:
>    - Rebase on latest changes in jump tables and crypto.
>    - Fix wording on couple commits.
>    - Revisit checkpatch warnings.
>    - Moving to @chromium.org.
>  - patch v5:
>    - Adapt new crypto modules for PIE.
>    - Improve per-cpu commit message.
>    - Fix xen 32-bit build error with .quad.
>    - Remove extra code for ftrace.
>  - patch v4:
>    - Simplify early boot by removing global variables.
>    - Modify the mcount location script for __mcount_loc intead of the address
>      read in the ftrace implementation.
>    - Edit commit description to explain better where the kernel can be located.
>    - Streamlined the testing done on each patch proposal. Always testing
>      hibernation, suspend, ftrace and kprobe to ensure no regressions.
>  - patch v3:
>    - Update on message to describe longer term PIE goal.
>    - Minor change on ftrace if condition.
>    - Changed code using xchgq.
>  - patch v2:
>    - Adapt patch to work post KPTI and compiler changes
>    - Redo all performance testing with latest configs and compilers
>    - Simplify mov macro on PIE (MOVABS now)
>    - Reduce GOT footprint
>  - 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 some of the changes necessary to build the kernel as
> Position Independent Executable (PIE) on x86_64. Another patchset will
> add the PIE option and larger architecture changes. PIE allows the kernel to be
> placed below the 0xffffffff80000000 increasing the range of KASLR.
> 
> The patches:
>  - 1, 3-11: Change in assembly code to be PIE compliant.
>  - 2: Add a new _ASM_MOVABS macro to fetch a symbol address generically.
> 
> diffstat:
>  crypto/aegis128-aesni-asm.S         |    6 +-
>  crypto/aesni-intel_asm.S            |    8 +--
>  crypto/aesni-intel_avx-x86_64.S     |    3 -
>  crypto/camellia-aesni-avx-asm_64.S  |   42 +++++++--------
>  crypto/camellia-aesni-avx2-asm_64.S |   44 ++++++++--------
>  crypto/camellia-x86_64-asm_64.S     |    8 +--
>  crypto/cast5-avx-x86_64-asm_64.S    |   50 ++++++++++--------
>  crypto/cast6-avx-x86_64-asm_64.S    |   44 +++++++++-------
>  crypto/des3_ede-asm_64.S            |   96 ++++++++++++++++++++++++------------
>  crypto/ghash-clmulni-intel_asm.S    |    4 -
>  crypto/glue_helper-asm-avx.S        |    4 -
>  crypto/glue_helper-asm-avx2.S       |    6 +-
>  crypto/sha256-avx2-asm.S            |   18 ++++--
>  entry/entry_64.S                    |   16 ++++--
>  include/asm/alternative.h           |    6 +-
>  include/asm/asm.h                   |    1 
>  include/asm/bug.h                   |    2 
>  include/asm/paravirt_types.h        |   32 ++++++++++--
>  include/asm/pm-trace.h              |    2 
>  include/asm/processor.h             |    6 +-
>  kernel/acpi/wakeup_64.S             |   31 ++++++-----
>  kernel/head_64.S                    |   15 +++--
>  kernel/relocate_kernel_64.S         |    2 
>  power/hibernate_asm_64.S            |    4 -
>  24 files changed, 268 insertions(+), 182 deletions(-)
> 
> Patchset is based on next-20200227.
> 
> 

-- 
Kees Cook