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