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

Kees Cook
2020-03-03T05:02:19Z

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