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arm64: kernel: Add support for Privileged Access Never

Vladimir Murzin linux-arm-kernel 1 version New

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Cover letter [PATCH v2 0/6] arm64: kernel: Add support for Privileged Access Never
Quoted 18 lines · James Morse

This series adds support for Privileged Access Never (PAN; part of the ARMv8.1 Extensions). When enabled, this feature causes a permission fault if the kernel attempts to access memory that is also accessible by userspace - instead the PAN bit must be cleared when accessing userspace memory. (or use the ldt*/stt* instructions).

This series detects and enables this feature, and uses alternatives to change {get,put}_user() et al to clear the PAN bit while they do their work.

Changes since v1:
* Copied cpuid_feature_extract_field() from arch/arm as a new patch, suggested by Russell King [1].
* Changed feature-detection patch to use cpuid_feature_extract_field() for sign extension, and '>='.
* Moved SCTLR_EL1_* from asm/cputype.h to asm/sysreg.h
* Added PSR_PAN_BIT in uapi/asm/ptrace.h
* Removed the setting of PSTATE_PAN in kernel/process.c

Quoted 2 lines

[1] http://www.spinics.net/lists/arm-kernel/msg432518.html

Hi James,

Looks like it doesn't play nicely with CONFIG_SWP_EMULATION=y. I get segfault while executing swp and PAN is enabled, though I've been playing with one of the older version.

Vladimir

Quoted 29 lines

James Morse (6):
arm64: kernel: Add cpuid_feature_extract_field() for 4bit sign
extension
arm64: kernel: preparatory: Move config_sctlr_el1
arm64: kernel: Add cpufeature 'enable' callback
arm64: kernel: Add min_register_value and use '>=' for feature
detection
arm64: kernel: Add optional CONFIG_ parameter to ALTERNATIVE()
arm64: kernel: Add support for Privileged Access Never

 arch/arm64/Kconfig                   | 14 +++++++++++++
 arch/arm64/include/asm/alternative.h | 28 ++++++++++++++++++++++---
 arch/arm64/include/asm/cpufeature.h  | 21 ++++++++++++++++---
 arch/arm64/include/asm/cputype.h     |  3 ---
 arch/arm64/include/asm/futex.h       |  8 ++++++++
 arch/arm64/include/asm/processor.h   |  2 ++
 arch/arm64/include/asm/sysreg.h      | 21 +++++++++++++++++++
 arch/arm64/include/asm/uaccess.h     | 11 ++++++++++
 arch/arm64/include/uapi/asm/ptrace.h |  1 +
 arch/arm64/kernel/armv8_deprecated.c | 11 +---------
 arch/arm64/kernel/cpufeature.c       | 40 +++++++++++++++++++++++++++++++++---
 arch/arm64/lib/clear_user.S          |  8 ++++++++
 arch/arm64/lib/copy_from_user.S      |  8 ++++++++
 arch/arm64/lib/copy_in_user.S        |  8 ++++++++
 arch/arm64/lib/copy_to_user.S        |  8 ++++++++
 arch/arm64/mm/fault.c                | 23 +++++++++++++++++++++
 16 files changed, 193 insertions(+), 22 deletions(-)

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