[PATCH 00/19] aarch64: Fix -fstack-protector issue

Richard Sandiford richard.sandiford@arm.com
Tue Sep 12 15:25:10 GMT 2023

This series of patches fixes deficiencies in GCC's -fstack-protector
implementation for AArch64 when using dynamically allocated stack space.
This is CVE-2023-4039.  See:


for more details.

The fix is to put the saved registers above the locals area when
-fstack-protector is used.

The series also fixes a stack-clash problem that I found while working
on the CVE.  In unpatched sources, the stack-clash problem would only
trigger for unrealistic numbers of arguments (8K 64-bit arguments, or an
equivalent).  But it would be a more significant issue with the new
-fstack-protector frame layout.  It's therefore important that both
problems are fixed together.

Some reorganisation of the code seemed necessary to fix the problems in a
cleanish way.  The series is therefore quite long, but only a handful of
patches should have any effect on code generation.

See the individual patches for a detailed description.

Tested on aarch64-linux-gnu. Pushed to trunk and to all active branches.
I've also pushed backports to GCC 7+ to vendors/ARM/heads/CVE-2023-4039.

Richard Sandiford (19):
  aarch64: Use local frame vars in shrink-wrapping code
  aarch64: Avoid a use of callee_offset
  aarch64: Explicitly handle frames with no saved registers
  aarch64: Add bytes_below_saved_regs to frame info
  aarch64: Add bytes_below_hard_fp to frame info
  aarch64: Tweak aarch64_save/restore_callee_saves
  aarch64: Only calculate chain_offset if there is a chain
  aarch64: Rename locals_offset to bytes_above_locals
  aarch64: Rename hard_fp_offset to bytes_above_hard_fp
  aarch64: Tweak frame_size comment
  aarch64: Measure reg_offset from the bottom of the frame
  aarch64: Simplify top of frame allocation
  aarch64: Minor initial adjustment tweak
  aarch64: Tweak stack clash boundary condition
  aarch64: Put LR save probe in first 16 bytes
  aarch64: Simplify probe of final frame allocation
  aarch64: Explicitly record probe registers in frame info
  aarch64: Remove below_hard_fp_saved_regs_size
  aarch64: Make stack smash canary protect saved registers

 gcc/config/aarch64/aarch64.cc                 | 518 ++++++++++--------
 gcc/config/aarch64/aarch64.h                  |  44 +-
 .../aarch64/stack-check-prologue-17.c         |  55 ++
 .../aarch64/stack-check-prologue-18.c         | 100 ++++
 .../aarch64/stack-check-prologue-19.c         | 100 ++++
 .../aarch64/stack-check-prologue-20.c         |   3 +
 .../gcc.target/aarch64/stack-protector-8.c    |  95 ++++
 .../gcc.target/aarch64/stack-protector-9.c    |  33 ++
 .../aarch64/sve/pcs/stack_clash_3.c           |   6 +-
 9 files changed, 699 insertions(+), 255 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-20.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-protector-8.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-protector-9.c


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