Re: [PATCH v7 20/39] arm64/gcs: Context switch GCS state for EL0

On Wed, Nov 22, 2023 at 1:45 AM Mark Brown broonie@kernel.org wrote:

+/*

• • Apply the GCS mode configured for the specified task to the
• • hardware.
• */

+void gcs_set_el0_mode(struct task_struct *task) +{

•   u64 gcscre0_el1 = GCSCRE0_EL1_nTR;
  

•   if (task->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE)
  

•           gcscre0_el1 |= GCSCRE0_EL1_RVCHKEN | GCSCRE0_EL1_PCRSEL;
  

If the intent is to disable, is the GCS stack freed or kept around? I expect if libc is taking the decision to disable, kernel should free it up. Is it freed in some other flow?

•   if (task->thread.gcs_el0_mode & PR_SHADOW_STACK_WRITE)
  

•           gcscre0_el1 |= GCSCRE0_EL1_STREn;
  

•   if (task->thread.gcs_el0_mode & PR_SHADOW_STACK_PUSH)
  

•           gcscre0_el1 |= GCSCRE0_EL1_PUSHMEn;
  

•   write_sysreg_s(gcscre0_el1, SYS_GCSCRE0_EL1);
  

+}