[PATCH 0/5] Improve arm64 pkeys handling in signal delivery

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This series is a follow-up to Joey's Permission Overlay Extension (POE)
series [1] that recently landed on mainline. The goal is to improve the
way we handle the register that governs which pkeys/POIndex are
accessible (POR_EL0) during signal delivery. As things stand, we may
unexpectedly fail to write the signal frame on the stack because POR_EL0
is not reset before the uaccess operations. See patch 3 for more details
and the main changes this series brings.

A similar series landed recently for x86/MPK [2]; the present series
aims at aligning arm64 with x86. Worth noting: once the signal frame is
written, POR_EL0 is still set to POR_EL0_INIT, granting access to pkey 0
only. This means that a program that sets up an alternate signal stack
with a non-zero pkey will need some assembly trampoline to set POR_EL0
before invoking the real signal handler, as discussed here [3].

The x86 series also added kselftests to ensure that no spurious SIGSEGV
occurs during signal delivery regardless of which pkey is accessible at
the point where the signal is delivered. This series adapts those
kselftests to allow running them on arm64 (patch 4-5).

Finally patch 2 is a clean-up following feedback on Joey's series [4].

I have tested this series on arm64 and x86_64 (booting and running the
protection_keys and pkey_sighandler_tests mm kselftests).

- Kevin

[1] https://lore.kernel.org/linux-arm-kernel/20240822151113.1479789-1-joey.gouly@xxxxxxx/
[2] https://lore.kernel.org/lkml/20240802061318.2140081-1-aruna.ramakrishna@xxxxxxxxxx/
[3] https://lore.kernel.org/lkml/CABi2SkWxNkP2O7ipkP67WKz0-LV33e5brReevTTtba6oKUfHRw@xxxxxxxxxxxxxx/
[4] https://lore.kernel.org/linux-arm-kernel/20241015114116.GA19334@willie-the-truck/

Cc: akpm@xxxxxxxxxxxxxxxxxxxx
Cc: anshuman.khandual@xxxxxxx
Cc: aruna.ramakrishna@xxxxxxxxxx
Cc: broonie@xxxxxxxxxx
Cc: catalin.marinas@xxxxxxx
Cc: dave.hansen@xxxxxxxxxxxxxxx
Cc: dave.martin@xxxxxxx
Cc: jeffxu@xxxxxxxxxxxx
Cc: joey.gouly@xxxxxxx
Cc: shuah@xxxxxxxxxx
Cc: will@xxxxxxxxxx
Cc: linux-kselftest@xxxxxxxxxxxxxxx
Cc: x86@xxxxxxxxxx

Kevin Brodsky (5):
  arm64: signal: Remove unused macro
  arm64: signal: Remove unnecessary check when saving POE state
  arm64: signal: Improve POR_EL0 handling to avoid uaccess failures
  selftests/mm: Use generic pkey register manipulation
  selftests/mm: Enable pkey_sighandler_tests on arm64

 arch/arm64/kernel/signal.c                    |  92 +++++++++++++---
 tools/testing/selftests/mm/Makefile           |   8 +-
 tools/testing/selftests/mm/pkey-arm64.h       |   1 +
 tools/testing/selftests/mm/pkey-x86.h         |   2 +
 .../selftests/mm/pkey_sighandler_tests.c      | 101 +++++++++++++-----
 5 files changed, 159 insertions(+), 45 deletions(-)

-- 
2.43.0





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