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       1                 :            : /* SPDX-License-Identifier: GPL-2.0 */
       2                 :            : /*
       3                 :            :  * GCC stack protector support.
       4                 :            :  *
       5                 :            :  * Stack protector works by putting predefined pattern at the start of
       6                 :            :  * the stack frame and verifying that it hasn't been overwritten when
       7                 :            :  * returning from the function.  The pattern is called stack canary
       8                 :            :  * and gcc expects it to be defined by a global variable called
       9                 :            :  * "__stack_chk_guard" on ARM.  This prevents SMP systems from using a
      10                 :            :  * different value for each task unless we enable a GCC plugin that
      11                 :            :  * replaces these symbol references with references to each task's own
      12                 :            :  * value.
      13                 :            :  */
      14                 :            : 
      15                 :            : #ifndef _ASM_STACKPROTECTOR_H
      16                 :            : #define _ASM_STACKPROTECTOR_H 1
      17                 :            : 
      18                 :            : #include <linux/random.h>
      19                 :            : #include <linux/version.h>
      20                 :            : 
      21                 :            : #include <asm/thread_info.h>
      22                 :            : 
      23                 :            : extern unsigned long __stack_chk_guard;
      24                 :            : 
      25                 :            : /*
      26                 :            :  * Initialize the stackprotector canary value.
      27                 :            :  *
      28                 :            :  * NOTE: this must only be called from functions that never return,
      29                 :            :  * and it must always be inlined.
      30                 :            :  */
      31                 :            : static __always_inline void boot_init_stack_canary(void)
      32                 :            : {
      33                 :            :         unsigned long canary;
      34                 :            : 
      35                 :            :         /* Try to get a semi random initial value. */
      36                 :        404 :         get_random_bytes(&canary, sizeof(canary));
      37                 :        404 :         canary ^= LINUX_VERSION_CODE;
      38                 :            : 
      39                 :        404 :         current->stack_canary = canary;
      40                 :            : #ifndef CONFIG_STACKPROTECTOR_PER_TASK
      41                 :        404 :         __stack_chk_guard = current->stack_canary;
      42                 :            : #else
      43                 :            :         current_thread_info()->stack_canary = current->stack_canary;
      44                 :            : #endif
      45                 :            : }
      46                 :            : 
      47                 :            : #endif  /* _ASM_STACKPROTECTOR_H */