[PATCH 0/4 v5] exec: inherit HWCAPs from the parent process

[Andrei Vagin <avagin@google.com>]

This patch series introduces a mechanism to inherit hardware capabilities
(AT_HWCAP, AT_HWCAP2, etc.) from a parent process when they have been
modified via prctl.

To support C/R operations (snapshots, live migration) in heterogeneous
clusters, we must ensure that processes utilize CPU features available
on all potential target nodes. To solve this, we need to advertise a
common feature set across the cluster.

Initially, a cgroup-based approach was considered, but it was decided
that inheriting HWCAPs from a parent process that has set its own
auxiliary vector via prctl is a simpler and more flexible solution.

This implementation adds a new mm flag MMF_USER_HWCAP, which is set when the
auxiliary vector is modified via prctl(PR_SET_MM_AUXV). When execve() is
called, if the current process has MMF_USER_HWCAP set, the HWCAP values are
extracted from the current auxiliary vector and inherited by the new process.

The first patch fixes AUXV size calculation for ELF_HWCAP3 and ELF_HWCAP4
in binfmt_elf_fdpic and updates AT_VECTOR_SIZE_BASE.

The second patch implements the core inheritance logic in execve().

The third patch adds a selftest to verify that HWCAPs are correctly
inherited across execve().

v5:
 -  Fix reading of HWCAPs from auxiliary vectors of compat processes.
 -  Defer HWCAP masking until ELF table creation (create_elf_tables)
    to handle compat process correctly.
 -  arm64: Disable HWCAP inheritance on architecture switch (e.g.,
    AArch64 to AArch32) by clearing MMF_USER_HWCAP, as HWCAP bits have
    completely different meanings across these architectures.

v4: minor fixes based on feedback from the previous version.
v3: synchronize saved_auxv access with arg_lock

v1: https://lkml.org/lkml/2025/12/5/65
v2: https://lkml.org/lkml/2026/1/8/219
v3: https://lkml.org/lkml/2026/2/9/1233
v4: https://lkml.org/lkml/2026/2/17/963

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chen Ridong <chenridong@huawei.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Koutny <mkoutny@suse.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>

Andrei Vagin (4):
  exec: inherit HWCAPs from the parent process
  arm64: elf: clear MMF_USER_HWCAP on architecture switch
  mm: synchronize saved_auxv access with arg_lock
  selftests/exec: add test for HWCAP inheritance

 arch/arm64/include/asm/elf.h                 |  12 ++-
 fs/binfmt_elf.c                              |  13 ++-
 fs/binfmt_elf_fdpic.c                        |  13 ++-
 fs/exec.c                                    |  54 ++++++++++
 fs/proc/base.c                               |  12 ++-
 include/linux/binfmts.h                      |  11 ++
 include/linux/mm_types.h                     |   3 +-
 kernel/fork.c                                |   8 ++
 kernel/sys.c                                 |  30 +++---
 tools/testing/selftests/exec/.gitignore      |   1 +
 tools/testing/selftests/exec/Makefile        |   1 +
 tools/testing/selftests/exec/hwcap_inherit.c | 105 +++++++++++++++++++
 12 files changed, 234 insertions(+), 29 deletions(-)
 create mode 100644 tools/testing/selftests/exec/hwcap_inherit.c

-- 
2.53.0.959.g497ff81fa9-goog