Linux Plumbers Conference 2021

Compiler Features for Kernel Security

24 Sept 2021, 10:05

30m

Microconference1/Virtual-Room (LPC Virtual)

Toolchains and Kernel MC Toolchains and Kernel MC

Speakers

Kees Cook (Google) Qing Zhao

Description

GCC and Clang both have a variety of security features available, but they are not always at parity with each other. This discussion will review the security features important to the Linux kernel with regard to what's working, what's missing, and what needs adjustment.

Specifically, these areas will be discussed along with anything else that seems relevant:

• stack protector guard location (i.e. enabling per-task canaries)

  -mstack-protector-guard=sysreg
  -mstack-protector-guard-reg=sp_el0
  -mstack-protector-guard-offset=0
  

• call-used register zeroing (now in GCC 11)

  -fzero-call-used-regs
  

• stack variable auto-initialization (already in Clang, soon to be in GCC 12)

  -ftrivial-auto-var-init={zero,pattern}
  

• array bounds checking

  -Warray-bounds
  -Wzero-length-bounds
  -Wzero-length-array
  -fsanitize=bounds
  -fsanitize=bounds-strict
  

• integer overflow protection

  -fsanitize=signed-integer-overflow
  -fsanitize=unsigned-integer-overflow
  

• Link Time Optimization

  -flto
  -flto=thin
  

• backward edge Control Flow Integrity

  -mbranch-protection=pac-ret[+leaf]
  -fsanitize=shadow-call-stack
  CET
  

• forward edge Control Flow Integrity

  -fcf-protection=branch
  -mbranch-protection=bti
  -fsanitize=cfi
  

• Spectre v1 mitigation

  -mspeculative-load-hardening
  

• structure layout randomization

  __attribute__((randomize_layout))
  

• constant expression for "is an lvalue?"

• constant expression for lvalue type extraction

Presentation materials

compiler-features-for-kernel-security.pdf