drivers/misc/lkdtm/stackleak.c

   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 <[email protected]>
   8  *   Tycho Andersen <[email protected]>
   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 stack
  17  * below this as expected.
  18  *
  19  * To prevent the lowest stack pointer changing during the test, IRQs are
  20  * masked and instrumentation of this function is disabled. We assume that the
  21  * 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 the
  24  * lowest stack pointer and/or clobbering poison values. To avoid spurious
  25  * failures we must avoid printing until the end of the test or have already
  26  * encountered a failure condition.
  27  */
  28 static 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 fall
  41          * within the expected task stack boundaries. These tests should never
  42          * fail unless the boundaries are incorrect or we're clobbering the
  43          * 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 recorded
  62          * 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 current
  66          * stack pointer might not be sufficiently aligned, we must align
  67          * downwards to find the lowest known stack pointer value. This is the
  68          * high boundary for a portion of the stack which may have been used
  69          * 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) consists
  81          * entirely of poison. This verifies the entries that
  82          * 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
 115 out:
 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
 124 static 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) */
 133 static 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
 143 static struct crashtype crashtypes[] = {
 144         CRASHTYPE(STACKLEAK_ERASING),
 145 };
 146
 147 struct crashtype_category stackleak_crashtypes = {
 148         .crashtypes = crashtypes,
 149         .len        = ARRAY_SIZE(crashtypes),
 150 };