text: // SPDX-License-Identifier: GPL-2.0
  /*
   * This code tests that the current task stack is properly erased (filled
   * with STACKLEAK_POISON).
   *
   * Authors:
   *   Alexander Popov <alex.popov@linux.com>
   *   Tycho Andersen <tycho@tycho.ws>
   */
  
  #include "lkdtm.h"
  #include <linux/stackleak.h>
  
  void lkdtm_STACKLEAK_ERASING(void)
  {
  	unsigned long *sp, left, found, i;
  	const unsigned long check_depth =
  			STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
  	bool test_failed = false;
  
  	/*
  	 * For the details about the alignment of the poison values, see
  	 * the comment in stackleak_track_stack().
  	 */
  	sp = PTR_ALIGN(&i, sizeof(unsigned long));
  
  	left = ((unsigned long)sp & (THREAD_SIZE - 1)) / sizeof(unsigned long);
  	sp--;
  
  	/*
  	 * One 'long int' at the bottom of the thread stack is reserved
  	 * and not poisoned.
  	 */
  	if (left > 1) {
  		left--;
  	} else {
  		pr_err("FAIL: not enough stack space for the test\n");
  		test_failed = true;
  		goto end;
  	}
  
  	pr_info("checking unused part of the thread stack (%lu bytes)...\n",
  					left * sizeof(unsigned long));
  
  	/*
  	 * Search for 'check_depth' poison values in a row (just like
  	 * stackleak_erase() does).
  	 */
  	for (i = 0, found = 0; i < left && found <= check_depth; i++) {
  		if (*(sp - i) == STACKLEAK_POISON)
  			found++;
  		else
  			found = 0;
  	}
  
  	if (found <= check_depth) {
  		pr_err("FAIL: the erased part is not found (checked %lu bytes)\n",
  						i * sizeof(unsigned long));
  		test_failed = true;
  		goto end;
  	}
  
  	pr_info("the erased part begins after %lu not poisoned bytes\n",
  				(i - found) * sizeof(unsigned long));
  
  	/* The rest of thread stack should be erased */
  	for (; i < left; i++) {
  		if (*(sp - i) != STACKLEAK_POISON) {
  			pr_err("FAIL: bad value number %lu in the erased part: 0x%lx\n",
  								i, *(sp - i));
  			test_failed = true;
  		}
  	}
  
  end:
  	if (test_failed) {
  		pr_err("FAIL: the thread stack is NOT properly erased\n");
  		dump_stack();
  	} else {
  		pr_info("OK: the rest of the thread stack is properly erased\n");
  	}
  }
  