misc/lkdtm/stackleak.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * This code tests that the current task stack is properly erased (filled
0004  * with STACKLEAK_POISON).
0005  *
0006  * Authors:
0007  *   Alexander Popov <alex.popov@linux.com>
0008  *   Tycho Andersen <tycho@tycho.ws>
0009  */
0010
0011 #include "lkdtm.h"
0012 #include <linux/stackleak.h>
0013
0014 #if defined(CONFIG_GCC_PLUGIN_STACKLEAK)
0015 /*
0016  * Check that stackleak tracks the lowest stack pointer and erases the stack
0017  * below this as expected.
0018  *
0019  * To prevent the lowest stack pointer changing during the test, IRQs are
0020  * masked and instrumentation of this function is disabled. We assume that the
0021  * compiler will create a fixed-size stack frame for this function.
0022  *
0023  * Any non-inlined function may make further use of the stack, altering the
0024  * lowest stack pointer and/or clobbering poison values. To avoid spurious
0025  * failures we must avoid printing until the end of the test or have already
0026  * encountered a failure condition.
0027  */
0028 static void noinstr check_stackleak_irqoff(void)
0029 {
0030     const unsigned long task_stack_base = (unsigned long)task_stack_page(current);
0031     const unsigned long task_stack_low = stackleak_task_low_bound(current);
0032     const unsigned long task_stack_high = stackleak_task_high_bound(current);
0033     const unsigned long current_sp = current_stack_pointer;
0034     const unsigned long lowest_sp = current->lowest_stack;
0035     unsigned long untracked_high;
0036     unsigned long poison_high, poison_low;
0037     bool test_failed = false;
0038
0039     /*
0040      * Check that the current and lowest recorded stack pointer values fall
0041      * within the expected task stack boundaries. These tests should never
0042      * fail unless the boundaries are incorrect or we're clobbering the
0043      * STACK_END_MAGIC, and in either casee something is seriously wrong.
0044      */
0045     if (current_sp < task_stack_low || current_sp >= task_stack_high) {
0046         pr_err("FAIL: current_stack_pointer (0x%lx) outside of task stack bounds [0x%lx..0x%lx]\n",
0047                current_sp, task_stack_low, task_stack_high - 1);
0048         test_failed = true;
0049         goto out;
0050     }
0051     if (lowest_sp < task_stack_low || lowest_sp >= task_stack_high) {
0052         pr_err("FAIL: current->lowest_stack (0x%lx) outside of task stack bounds [0x%lx..0x%lx]\n",
0053                lowest_sp, task_stack_low, task_stack_high - 1);
0054         test_failed = true;
0055         goto out;
0056     }
0057
0058     /*
0059      * Depending on what has run prior to this test, the lowest recorded
0060      * stack pointer could be above or below the current stack pointer.
0061      * Start from the lowest of the two.
0062      *
0063      * Poison values are naturally-aligned unsigned longs. As the current
0064      * stack pointer might not be sufficiently aligned, we must align
0065      * downwards to find the lowest known stack pointer value. This is the
0066      * high boundary for a portion of the stack which may have been used
0067      * without being tracked, and has to be scanned for poison.
0068      */
0069     untracked_high = min(current_sp, lowest_sp);
0070     untracked_high = ALIGN_DOWN(untracked_high, sizeof(unsigned long));
0071
0072     /*
0073      * Find the top of the poison in the same way as the erasing code.
0074      */
0075     poison_high = stackleak_find_top_of_poison(task_stack_low, untracked_high);
0076
0077     /*
0078      * Check whether the poisoned portion of the stack (if any) consists
0079      * entirely of poison. This verifies the entries that
0080      * stackleak_find_top_of_poison() should have checked.
0081      */
0082     poison_low = poison_high;
0083     while (poison_low > task_stack_low) {
0084         poison_low -= sizeof(unsigned long);
0085
0086         if (*(unsigned long *)poison_low == STACKLEAK_POISON)
0087             continue;
0088
0089         pr_err("FAIL: non-poison value %lu bytes below poison boundary: 0x%lx\n",
0090                poison_high - poison_low, *(unsigned long *)poison_low);
0091         test_failed = true;
0092     }
0093
0094     pr_info("stackleak stack usage:\n"
0095         "  high offset: %lu bytes\n"
0096         "  current:     %lu bytes\n"
0097         "  lowest:      %lu bytes\n"
0098         "  tracked:     %lu bytes\n"
0099         "  untracked:   %lu bytes\n"
0100         "  poisoned:    %lu bytes\n"
0101         "  low offset:  %lu bytes\n",
0102         task_stack_base + THREAD_SIZE - task_stack_high,
0103         task_stack_high - current_sp,
0104         task_stack_high - lowest_sp,
0105         task_stack_high - untracked_high,
0106         untracked_high - poison_high,
0107         poison_high - task_stack_low,
0108         task_stack_low - task_stack_base);
0109
0110 out:
0111     if (test_failed) {
0112         pr_err("FAIL: the thread stack is NOT properly erased!\n");
0113     } else {
0114         pr_info("OK: the rest of the thread stack is properly erased\n");
0115     }
0116 }
0117
0118 static void lkdtm_STACKLEAK_ERASING(void)
0119 {
0120     unsigned long flags;
0121
0122     local_irq_save(flags);
0123     check_stackleak_irqoff();
0124     local_irq_restore(flags);
0125 }
0126 #else /* defined(CONFIG_GCC_PLUGIN_STACKLEAK) */
0127 static void lkdtm_STACKLEAK_ERASING(void)
0128 {
0129     if (IS_ENABLED(CONFIG_HAVE_ARCH_STACKLEAK)) {
0130         pr_err("XFAIL: stackleak is not enabled (CONFIG_GCC_PLUGIN_STACKLEAK=n)\n");
0131     } else {
0132         pr_err("XFAIL: stackleak is not supported on this arch (HAVE_ARCH_STACKLEAK=n)\n");
0133     }
0134 }
0135 #endif /* defined(CONFIG_GCC_PLUGIN_STACKLEAK) */
0136
0137 static struct crashtype crashtypes[] = {
0138     CRASHTYPE(STACKLEAK_ERASING),
0139 };
0140
0141 struct crashtype_category stackleak_crashtypes = {
0142     .crashtypes = crashtypes,
0143     .len        = ARRAY_SIZE(crashtypes),
0144 };