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 14 void 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 75 end: 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