[all-commits] [llvm/llvm-project] d7e8a7: [AArch64][PAC] Lower auth/resign into checked sequ...

[Ahmed Bougacha via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d7e8a7487cd793df0fdf51a94afc25ab0a325a9a
      https://github.com/llvm/llvm-project/commit/d7e8a7487cd793df0fdf51a94afc25ab0a325a9a
  Author: Ahmed Bougacha <ahmed at bougacha.org>
  Date:   2024-07-22 (Mon, 22 Jul 2024)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
    M llvm/lib/Target/AArch64/AArch64Features.td
    M llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
    M llvm/lib/Target/AArch64/AArch64InstrInfo.td
    M llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
    A llvm/test/CodeGen/AArch64/ptrauth-fpac.ll
    A llvm/test/CodeGen/AArch64/ptrauth-intrinsic-auth-resign-with-blend.ll
    A llvm/test/CodeGen/AArch64/ptrauth-intrinsic-auth-resign.ll

  Log Message:
  -----------
  [AArch64][PAC] Lower auth/resign into checked sequence. (#79024)

This introduces 3 hardening modes in the authentication step of
auth/resign lowering:
- unchecked, which uses the AUT instructions as-is
- poison, which detects authentication failure (using an XPAC+CMP
  sequence), explicitly yielding the XPAC result rather than the
  AUT result, to avoid leaking
- trap, which additionally traps on authentication failure,
  using BRK #0xC470 + key (IA C470, IB C471, DA C472, DB C473.)

Not all modes are necessarily useful in all contexts, and there
are more performant alternative lowerings in specific contexts
(e.g., when I/D TBI enablement is a target ABI guarantee.)
These will be implemented separately.

This is controlled by the `ptrauth-auth-traps` function attributes,
and can be overridden using `-aarch64-ptrauth-auth-checks=`.

This also adds the FPAC extension, which we haven't needed
before, to improve isel when we can rely on HW checking.



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