ARM: add vmap'ed stack support

This series enables support on ARM for vmap'ed task and IRQ stacks in the kernel. This is an important hardening feature that terminates tasks on inadvertent or deliberate accesses past the stack pointer, which might otherwise go completely unnoticed.

Since having an accurate backtrace is especially important in such cases, this series includes some enhancements to the unwinder and to some hand rolled unwind info to increase the likelihood that a backtrace can be generated when relying on the ARM unwinder. The frame pointer unwinder turns out to be rather bullet proof in this context, and does not need any such enhancements.

According to a quick survey I did, compiler generated code puts a single stack push as the first instruction in about 2/3 of the cases, which the unwinder can deal with after applying patch #4, even if this push faulted because of a stack overflow. In the remaining cases, the compiler tends to fall back to R11 or R7 as the frame pointer (on ARM or Thumb-2, respectively), or emit partial unwind frames for the part of the function that runs before the stack frame is set up, and the part that runs inside the stack frame. In either case, the unwinder can deal with such occurrences as they don't rely on the stack pointer directly.

Changes since v3:
- avoid using the wrong virtual to physical translation on the stack pointer in the suspend/cpuidle code path,
- check whether SP points into the linear map rather than whether it points into the overflow stack specifically, so that other stacks are disregarded as well,
- use a per-CPU pointer rather than a per-CPU allocation for the overflow stack, so the stack itself can be allocated via the page allocator,
- avoid deliberately corrupting any task userland state, by repurposing the padding in the per-mode stacks as scratch space to hold a single GPR value, and rejigging the __bad_stack handler to only require a single GPR to load the overflow stack address into SP.

Changes since v2:
- rebase onto v5.16-rc1
- incorporate Nico's review feedback

Changes since v1:
- handle a missed corner case in svc_entry code, and while at it, streamline it a bit, especially for Thumb-2, which no longer needs to move SP into R0 twice to do the overflow check and the alignment check,
- improve the memcpy patch so that we no longer need to push the frame pointer separately,
- add Keith's tested-by

Patches #1, #2 and #3 update the ARM asm string routines to align more closely with the compiler's approach in terms of unwind tables, increasing the likelihood that we can unwind them in case of a stack overflow.

Patches #5 and #6 do some preparatory refactoring for the entry and switch_to code, to reduce clutter in patch #7.

Patch #7 wires up the generic support, and adds the entry code to detect and deal with stack overflows.

This series applies onto my IRQ stacks series sent out earlier:
https://lore.kernel.org/linux-arm-kernel/[email protected]/

Ard Biesheuvel (7):
ARM: memcpy: use frame pointer as unwind anchor
ARM: memmove: use frame pointer as unwind anchor
ARM: memset: clean up unwind annotations
ARM: unwind: disregard unwind info before stack frame is set up
ARM: switch_to: clean up Thumb2 code path
ARM: entry: rework stack realignment code in svc_entry
ARM: implement support for vmap'ed stacks

 arch/arm/Kconfig                   |   1 +
 arch/arm/include/asm/page.h        |   4 +
 arch/arm/include/asm/thread_info.h |   8 ++
 arch/arm/kernel/entry-armv.S       | 139 +++++++++++++++++---
 arch/arm/kernel/entry-header.S     |  37 ++++++
 arch/arm/kernel/irq.c              |   9 +-
 arch/arm/kernel/setup.c            |   8 +-
 arch/arm/kernel/sleep.S            |   8 ++
 arch/arm/kernel/traps.c            |  80 ++++++++++-
 arch/arm/kernel/unwind.c           |  19 ++-
 arch/arm/kernel/vmlinux.lds.S      |   4 +-
 arch/arm/lib/copy_from_user.S      |  13 +-
 arch/arm/lib/copy_template.S       |  67 ++++------
 arch/arm/lib/copy_to_user.S        |  13 +-
 arch/arm/lib/memcpy.S              |  13 +-
 arch/arm/lib/memmove.S             |  60 +++------
 arch/arm/lib/memset.S              |   7 +-
 17 files changed, 349 insertions(+), 141 deletions(-)

2.30.2

_______________________________________________
linux-arm-kernel mailing list
[email protected]
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel