linux/drivers/misc/lkdtm/stackleak.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * This code tests that the current task stack is properly erased (filled
   4 * with STACKLEAK_POISON).
   5 *
   6 * Authors:
   7 *   Alexander Popov <alex.popov@linux.com>
   8 *   Tycho Andersen <tycho@tycho.ws>
   9 */
  10
  11#include "lkdtm.h"
  12#include <linux/stackleak.h>
  13
  14void lkdtm_STACKLEAK_ERASING(void)
  15{
  16        unsigned long *sp, left, found, i;
  17        const unsigned long check_depth =
  18                        STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
  19        bool test_failed = false;
  20
  21        /*
  22         * For the details about the alignment of the poison values, see
  23         * the comment in stackleak_track_stack().
  24         */
  25        sp = PTR_ALIGN(&i, sizeof(unsigned long));
  26
  27        left = ((unsigned long)sp & (THREAD_SIZE - 1)) / sizeof(unsigned long);
  28        sp--;
  29
  30        /*
  31         * One 'long int' at the bottom of the thread stack is reserved
  32         * and not poisoned.
  33         */
  34        if (left > 1) {
  35                left--;
  36        } else {
  37                pr_err("FAIL: not enough stack space for the test\n");
  38                test_failed = true;
  39                goto end;
  40        }
  41
  42        pr_info("checking unused part of the thread stack (%lu bytes)...\n",
  43                                        left * sizeof(unsigned long));
  44
  45        /*
  46         * Search for 'check_depth' poison values in a row (just like
  47         * stackleak_erase() does).
  48         */
  49        for (i = 0, found = 0; i < left && found <= check_depth; i++) {
  50                if (*(sp - i) == STACKLEAK_POISON)
  51                        found++;
  52                else
  53                        found = 0;
  54        }
  55
  56        if (found <= check_depth) {
  57                pr_err("FAIL: the erased part is not found (checked %lu bytes)\n",
  58                                                i * sizeof(unsigned long));
  59                test_failed = true;
  60                goto end;
  61        }
  62
  63        pr_info("the erased part begins after %lu not poisoned bytes\n",
  64                                (i - found) * sizeof(unsigned long));
  65
  66        /* The rest of thread stack should be erased */
  67        for (; i < left; i++) {
  68                if (*(sp - i) != STACKLEAK_POISON) {
  69                        pr_err("FAIL: bad value number %lu in the erased part: 0x%lx\n",
  70                                                                i, *(sp - i));
  71                        test_failed = true;
  72                }
  73        }
  74
  75end:
  76        if (test_failed) {
  77                pr_err("FAIL: the thread stack is NOT properly erased!\n");
  78                pr_expected_config(CONFIG_GCC_PLUGIN_STACKLEAK);
  79        } else {
  80                pr_info("OK: the rest of the thread stack is properly erased\n");
  81        }
  82}
  83