x86: cleanup stack protector

Impact: cleanup

Make the following cleanups.

* remove duplicate comment from boot_init_stack_canary() which fits
  better in the other place - cpu_idle().

* move stack_canary offset check from __switch_to() to
  boot_init_stack_canary().

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 6 insertions, 7 deletions

diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index c7f0d10bae7b..2383e5bb475c 100644
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h
@@ -16,13 +16,12 @@ static __always_inline void boot_init_stack_canary(void)
         u64 tsc;
 
         /*
-         * If we're the non-boot CPU, nothing set the PDA stack
-         * canary up for us - and if we are the boot CPU we have
-         * a 0 stack canary. This is a good place for updating
-         * it, as we wont ever return from this function (so the
-         * invalid canaries already on the stack wont ever
-         * trigger).
-         *
+         * Build time only check to make sure the stack_canary is at
+         * offset 40 in the pda; this is a gcc ABI requirement
+         */
+        BUILD_BUG_ON(offsetof(struct x8664_pda, stack_canary) != 40);
+
+        /*
          * We both use the random pool and the current TSC as a source
          * of randomness. The TSC only matters for very early init,
          * there it already has some randomness on most systems. Later