[PATCH v4 0/5] ARM: support THREAD_INFO_IN_TASK

Placing thread_info in the kernel stack leaves it vulnerable to stack
overflow attacks. This short series addresses that by using the existing
THREAD_INFO_IN_TASK infrastructure.

This v4 is a follow-up to Keith's v3 [0], which did not address all
concerns I raised in response to v2. After collaborating with Keith
off-list, we decided that I should go ahead and post our joint v4.

Changes since v3:

- Leave the CPU field in thread_info, and keep it in sync at context
  switch time. This is by far the easiest and cleanest way to work
  around the fact that it is infeasible to implement
  raw_smp_processor_id() in terms of task_struct::cpu (for reasons of
  header soup).

- Drop the VFP changes, they are no longer necessary given the previous
  point.

- Drop the change to pass the CPU number to secondary_start_kernel().
  Given that we also need to pass the idle task pointer, which carries
  the CPU number, passing the CPU number directly is redundant.

- Use the TPIDRURO register to carry 'current' while running in the
  kernel, and keep using TPIDRPRW for the per-CPU offset as before. This
  way, there is no need to make any changes to the way the per-CPU offsets
  are programmed. It also avoids the concurrency issues that would
  result from carrying the 'current' pointer in a per-CPU variable.

- Update the per-task stack protector plugin to pull the stack canary
  value directly from the task struct.

Cc: Keith Packard <redacted>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Kees Cook <redacted>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Walleij <redacted>

[0] https://lore.kernel.org/all/20210907220038.91021-1-keithpac@amazon.com/ (local)

Ard Biesheuvel (4):
  gcc-plugins: arm-ssp: Prepare for THREAD_INFO_IN_TASK support
  ARM: smp: Free up the TLS register while running in the kernel
  ARM: smp: Store current pointer in TPIDRURO register if available
  ARM: smp: Enable THREAD_INFO_IN_TASK

Keith Packard (1):
  ARM: smp: Pass task to secondary_start_kernel

 arch/arm/Kconfig                              |  8 ++-
 arch/arm/Makefile                             |  5 +-
 arch/arm/include/asm/assembler.h              | 29 +++++++++++
 arch/arm/include/asm/current.h                | 51 ++++++++++++++++++++
 arch/arm/include/asm/smp.h                    |  3 +-
 arch/arm/include/asm/stackprotector.h         |  2 -
 arch/arm/include/asm/switch_to.h              | 16 ++++++
 arch/arm/include/asm/thread_info.h            | 15 ++++--
 arch/arm/include/asm/tls.h                    | 10 ++--
 arch/arm/kernel/asm-offsets.c                 |  6 +--
 arch/arm/kernel/entry-armv.S                  |  8 ++-
 arch/arm/kernel/entry-common.S                |  1 +
 arch/arm/kernel/entry-header.S                |  8 +++
 arch/arm/kernel/head-common.S                 |  5 ++
 arch/arm/kernel/head-nommu.S                  |  1 +
 arch/arm/kernel/head.S                        |  5 +-
 arch/arm/kernel/process.c                     |  8 +--
 arch/arm/kernel/smp.c                         | 13 ++++-
 arch/arm/mm/proc-macros.S                     |  3 +-
 scripts/gcc-plugins/arm_ssp_per_task_plugin.c | 27 +++--------
 20 files changed, 173 insertions(+), 51 deletions(-)
 create mode 100644 arch/arm/include/asm/current.h

-- 
2.30.2


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