[PATCH] D81402: [AArch64] Extend AArch64SLSHardeningPass to harden BLR instructions.

[Kristof Beyls via Phabricator via llvm-commits]

kristof.beyls created this revision.
kristof.beyls added a reviewer: ostannard.
Herald added subscribers: llvm-commits, danielkiss, hiraditya.
Herald added a project: LLVM.

To make sure that no barrier gets placed on the architectural execution
path, each

  BLR x<N>

instruction gets transformed to a

  BL __llvm_slsblr_thunk_x<N>

instruction, with __llvm_slsblr_thunk_x<N> a thunk that contains
__llvm_slsblr_thunk_x<N>:

  BR x<N>
  <speculation barrier>

Therefore, the BLR instruction gets split into 2; one BL and one BR.
This transformation results in not inserting a speculation barrier on
the architectural execution path.

The mitigation is off by default and can be enabled by the
harden-sls-blr subtarget feature.

As BLRA* indirect calls are not produced by LLVM currently, this does
not aim to implement support for those.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D81402

Files:
  llvm/lib/Target/AArch64/AArch64.h
  llvm/lib/Target/AArch64/AArch64.td
  llvm/lib/Target/AArch64/AArch64SLSHardening.cpp
  llvm/lib/Target/AArch64/AArch64Subtarget.h
  llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
  llvm/test/CodeGen/AArch64/O0-pipeline.ll
  llvm/test/CodeGen/AArch64/O3-pipeline.ll
  llvm/test/CodeGen/AArch64/speculation-hardening-sls-blr.mir
  llvm/test/CodeGen/AArch64/speculation-hardening-sls.ll

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