Re: [PATCH v7 25/39] arm64/signal: Expose GCS state in signal frames

Mark Brown broonie@kernel.org writes:

+static int preserve_gcs_context(struct gcs_context __user *ctx) +{

• int err = 0;
• u64 gcspr;
• /*

• * We will add a cap token to the frame, include it in the
  

• * GCSPR_EL0 we report to support stack switching via
  

• * sigreturn.
  

• */
  

• gcs_preserve_current_state();
• gcspr = current->thread.gcspr_el0;
• if (task_gcs_el0_enabled(current))

• gcspr -= 8;
  

• __put_user_error(GCS_MAGIC, &ctx->head.magic, err);
• __put_user_error(sizeof(*ctx), &ctx->head.size, err);
• __put_user_error(gcspr, &ctx->gcspr, err);
• __put_user_error(current->thread.gcs_el0_mode,

• 	 &ctx->features_enabled, err);
  

Other preserve_<foo>_context() functions zero the reserved fields in ctx. I suggest doing the same here. It helps with backward compatibility.

• return err;

+}