[PATCH v4 0/7] support FEAT_MTE_STORE_ONLY feature

[Yeoreum Yun]

ARMv8.5 based processors introduce the Memory Tagging Extension (MTE) feature.
MTE is built on top of the ARMv8.0 virtual address tagging TBI
(Top Byte Ignore) feature and allows software to access a 4-bit
allocation tag for each 16-byte granule in the physical address space.
A logical tag is derived from bits 59-56 of the virtual
address used for the memory access. A CPU with MTE enabled will compare
the logical tag against the allocation tag and potentially raise an
tag check fault on mismatch, subject to system registers configuration.

Since ARMv8.9, FEAT_MTE_STORE_ONLY can be used to restrict raise of tag
check fault on store operation only.
For this, application can use PR_MTE_STORE_ONLY flag
when it sets the MTE setting with prctl().

This feature omits tag check for fetch/read operation.
So it might be used not only debugging purpose but also be used
by application requiring strong memory safty in normal env.

Patch Sequences
================

Patch #1 adds cpufeature FEAT_MTE_STORE_ONLY

Patch #2 introduce new flag -- PR_MTE_STORE_ONLY

Patch #3 support MTE_STORE_ONLY feature

Patch #4 add HWCAP for MTE_STORE_ONLY

Patch #5 adds mte store-only hwcap test

Patch #6 preparation for adding mte store-only testcase

Patch #7 adds mte store-only testcases

Patch History
================

v3 to v4:
  - separate cpufeature and hwcap commit.
  - add mte store-only testcases in check_mmap_options
  - https://lore.kernel.org/linux-arm-kernel/aApBk8eGA2Eo57fq@e129823.arm.com/

v2 to v3:
  - rebase to 6.15-rc1
  - https://lore.kernel.org/linux-arm-kernel/20250403174701.74312-1-yeoreum.yun@arm.com/

v1 to v2:
  - add doc to elf_hwcaps.rst
  - add MTE_STORE_ONLY hwcap test
  - https://lore.kernel.org/linux-arm-kernel/20250403142707.26397-1-yeoreum.yun@arm.com/

Note:
  This patch based on
    https://lore.kernel.org/linux-arm-kernel/20250507095757.1663684-1-yeoreum.yun@arm.com/

Yeoreum Yun (7):
  arm64/cpufeature: add MTE_STORE_ONLY feature
  prtcl: introduce PR_MTE_STORE_ONLY
  arm64/kernel: support store-only mte tag check
  arm64/hwcaps: add MTE_STORE_ONLY hwcaps
  tools/kselftest: add MTE_STORE_ONLY feature hwcap test
  kselftest/arm64/mte: preparation for mte store only test
  kselftest/arm64/mte: add MTE_STORE_ONLY testcases

 Documentation/arch/arm64/elf_hwcaps.rst       |   3 +
 arch/arm64/include/asm/hwcap.h                |   1 +
 arch/arm64/include/asm/processor.h            |   2 +
 arch/arm64/include/uapi/asm/hwcap.h           |   1 +
 arch/arm64/kernel/cpufeature.c                |   9 ++
 arch/arm64/kernel/cpuinfo.c                   |   1 +
 arch/arm64/kernel/mte.c                       |  11 +-
 arch/arm64/kernel/process.c                   |   6 +-
 arch/arm64/tools/cpucaps                      |   1 +
 include/uapi/linux/prctl.h                    |   2 +
 tools/testing/selftests/arm64/abi/hwcap.c     |   6 +
 .../selftests/arm64/mte/check_buffer_fill.c   |  10 +-
 .../selftests/arm64/mte/check_child_memory.c  |   4 +-
 .../arm64/mte/check_hugetlb_options.c         |   6 +-
 .../selftests/arm64/mte/check_ksm_options.c   |   2 +-
 .../selftests/arm64/mte/check_mmap_options.c  | 116 ++++++++++++------
 .../testing/selftests/arm64/mte/check_prctl.c |  25 ++--
 .../arm64/mte/check_tags_inclusion.c          |   8 +-
 .../selftests/arm64/mte/check_user_mem.c      |   2 +-
 .../selftests/arm64/mte/mte_common_util.c     |  14 ++-
 .../selftests/arm64/mte/mte_common_util.h     |   3 +-
 21 files changed, 167 insertions(+), 66 deletions(-)

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