x86: stackprotector: mix TSC to the boot canary

mix the TSC to the boot canary.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 17 insertions, 3 deletions

diff --git a/include/asm-x86/stackprotector.h b/include/asm-x86/stackprotector.h
index 0f91f7a2688..3baf7ad89be 100644
--- a/include/asm-x86/stackprotector.h
+++ b/include/asm-x86/stackprotector.h
@@ -1,6 +1,8 @@
 #ifndef _ASM_STACKPROTECTOR_H
 #define _ASM_STACKPROTECTOR_H 1
 
+#include <asm/tsc.h>
+
 /*
  * Initialize the stackprotector canary value.
  *
@@ -9,16 +11,28 @@
  */
 static __always_inline void boot_init_stack_canary(void)
 {
+        u64 canary;
+        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):
+         * trigger).
+         *
+         * 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
+         * on during the bootup the random pool has true entropy too.
          */
-        current->stack_canary = get_random_int();
-        write_pda(stack_canary, current->stack_canary);
+        get_random_bytes(&canary, sizeof(canary));
+        tsc = __native_read_tsc();
+        canary += tsc + (tsc << 32UL);
+
+        current->stack_canary = canary;
+        write_pda(stack_canary, canary);
 }
 
 #endif