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1// SPDX-License-Identifier: GPL-2.02/*3 * This code tests that the current task stack is properly erased (filled4 * 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#if defined(CONFIG_GCC_PLUGIN_STACKLEAK)15/*16 * Check that stackleak tracks the lowest stack pointer and erases the stack17 * below this as expected.18 *19 * To prevent the lowest stack pointer changing during the test, IRQs are20 * masked and instrumentation of this function is disabled. We assume that the21 * compiler will create a fixed-size stack frame for this function.22 *23 * Any non-inlined function may make further use of the stack, altering the24 * lowest stack pointer and/or clobbering poison values. To avoid spurious25 * failures we must avoid printing until the end of the test or have already26 * encountered a failure condition.27 */28static void noinstr check_stackleak_irqoff(void)29{30 const unsigned long task_stack_base = (unsigned long)task_stack_page(current);31 const unsigned long task_stack_low = stackleak_task_low_bound(current);32 const unsigned long task_stack_high = stackleak_task_high_bound(current);33 const unsigned long current_sp = current_stack_pointer;34 const unsigned long lowest_sp = current->lowest_stack;35 unsigned long untracked_high;36 unsigned long poison_high, poison_low;37 bool test_failed = false;38 39 /*40 * Check that the current and lowest recorded stack pointer values fall41 * within the expected task stack boundaries. These tests should never42 * fail unless the boundaries are incorrect or we're clobbering the43 * STACK_END_MAGIC, and in either casee something is seriously wrong.44 */45 if (current_sp < task_stack_low || current_sp >= task_stack_high) {46 instrumentation_begin();47 pr_err("FAIL: current_stack_pointer (0x%lx) outside of task stack bounds [0x%lx..0x%lx]\n",48 current_sp, task_stack_low, task_stack_high - 1);49 test_failed = true;50 goto out;51 }52 if (lowest_sp < task_stack_low || lowest_sp >= task_stack_high) {53 instrumentation_begin();54 pr_err("FAIL: current->lowest_stack (0x%lx) outside of task stack bounds [0x%lx..0x%lx]\n",55 lowest_sp, task_stack_low, task_stack_high - 1);56 test_failed = true;57 goto out;58 }59 60 /*61 * Depending on what has run prior to this test, the lowest recorded62 * stack pointer could be above or below the current stack pointer.63 * Start from the lowest of the two.64 *65 * Poison values are naturally-aligned unsigned longs. As the current66 * stack pointer might not be sufficiently aligned, we must align67 * downwards to find the lowest known stack pointer value. This is the68 * high boundary for a portion of the stack which may have been used69 * without being tracked, and has to be scanned for poison.70 */71 untracked_high = min(current_sp, lowest_sp);72 untracked_high = ALIGN_DOWN(untracked_high, sizeof(unsigned long));73 74 /*75 * Find the top of the poison in the same way as the erasing code.76 */77 poison_high = stackleak_find_top_of_poison(task_stack_low, untracked_high);78 79 /*80 * Check whether the poisoned portion of the stack (if any) consists81 * entirely of poison. This verifies the entries that82 * stackleak_find_top_of_poison() should have checked.83 */84 poison_low = poison_high;85 while (poison_low > task_stack_low) {86 poison_low -= sizeof(unsigned long);87 88 if (*(unsigned long *)poison_low == STACKLEAK_POISON)89 continue;90 91 instrumentation_begin();92 pr_err("FAIL: non-poison value %lu bytes below poison boundary: 0x%lx\n",93 poison_high - poison_low, *(unsigned long *)poison_low);94 test_failed = true;95 goto out;96 }97 98 instrumentation_begin();99 pr_info("stackleak stack usage:\n"100 " high offset: %lu bytes\n"101 " current: %lu bytes\n"102 " lowest: %lu bytes\n"103 " tracked: %lu bytes\n"104 " untracked: %lu bytes\n"105 " poisoned: %lu bytes\n"106 " low offset: %lu bytes\n",107 task_stack_base + THREAD_SIZE - task_stack_high,108 task_stack_high - current_sp,109 task_stack_high - lowest_sp,110 task_stack_high - untracked_high,111 untracked_high - poison_high,112 poison_high - task_stack_low,113 task_stack_low - task_stack_base);114 115out:116 if (test_failed) {117 pr_err("FAIL: the thread stack is NOT properly erased!\n");118 } else {119 pr_info("OK: the rest of the thread stack is properly erased\n");120 }121 instrumentation_end();122}123 124static void lkdtm_STACKLEAK_ERASING(void)125{126 unsigned long flags;127 128 local_irq_save(flags);129 check_stackleak_irqoff();130 local_irq_restore(flags);131}132#else /* defined(CONFIG_GCC_PLUGIN_STACKLEAK) */133static void lkdtm_STACKLEAK_ERASING(void)134{135 if (IS_ENABLED(CONFIG_HAVE_ARCH_STACKLEAK)) {136 pr_err("XFAIL: stackleak is not enabled (CONFIG_GCC_PLUGIN_STACKLEAK=n)\n");137 } else {138 pr_err("XFAIL: stackleak is not supported on this arch (HAVE_ARCH_STACKLEAK=n)\n");139 }140}141#endif /* defined(CONFIG_GCC_PLUGIN_STACKLEAK) */142 143static struct crashtype crashtypes[] = {144 CRASHTYPE(STACKLEAK_ERASING),145};146 147struct crashtype_category stackleak_crashtypes = {148 .crashtypes = crashtypes,149 .len = ARRAY_SIZE(crashtypes),150};151