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// SPDX-License-Identifier: GPL-2.0
/*
* This code tests that the current task stack is properly erased (filled
* with STACKLEAK_POISON).
*
* Authors:
* Alexander Popov <alex.popov@linux.com>
* Tycho Andersen <tycho@tycho.ws>
*/
#include "lkdtm.h"
#include <linux/stackleak.h>
/*
* Check that stackleak tracks the lowest stack pointer and erases the stack
* below this as expected.
*
* To prevent the lowest stack pointer changing during the test, IRQs are
* masked and instrumentation of this function is disabled. We assume that the
* compiler will create a fixed-size stack frame for this function.
*
* Any non-inlined function may make further use of the stack, altering the
* lowest stack pointer and/or clobbering poison values. To avoid spurious
* failures we must avoid printing until the end of the test or have already
* encountered a failure condition.
*/
static void noinstr check_stackleak_irqoff(void)
{
const unsigned long task_stack_base = (unsigned long)task_stack_page(current);
const unsigned long task_stack_low = stackleak_task_low_bound(current);
const unsigned long task_stack_high = stackleak_task_high_bound(current);
const unsigned long current_sp = current_stack_pointer;
const unsigned long lowest_sp = current->lowest_stack;
unsigned long untracked_high;
unsigned long poison_high, poison_low;
bool test_failed = false;
/*
* Depending on what has run prior to this test, the lowest recorded
* stack pointer could be above or below the current stack pointer.
* Start from the lowest of the two.
*
* Poison values are naturally-aligned unsigned longs. As the current
* stack pointer might not be sufficiently aligned, we must align
* downwards to find the lowest known stack pointer value. This is the
* high boundary for a portion of the stack which may have been used
* without being tracked, and has to be scanned for poison.
*/
untracked_high = min(current_sp, lowest_sp);
untracked_high = ALIGN_DOWN(untracked_high, sizeof(unsigned long));
/*
* Find the top of the poison in the same way as the erasing code.
*/
poison_high = stackleak_find_top_of_poison(task_stack_low, untracked_high);
/*
* Check whether the poisoned portion of the stack (if any) consists
* entirely of poison. This verifies the entries that
* stackleak_find_top_of_poison() should have checked.
*/
poison_low = poison_high;
while (poison_low > task_stack_low) {
poison_low -= sizeof(unsigned long);
if (*(unsigned long *)poison_low == STACKLEAK_POISON)
continue;
pr_err("FAIL: non-poison value %lu bytes below poison boundary: 0x%lx\n",
poison_high - poison_low, *(unsigned long *)poison_low);
test_failed = true;
}
pr_info("stackleak stack usage:\n"
" high offset: %lu bytes\n"
" current: %lu bytes\n"
" lowest: %lu bytes\n"
" tracked: %lu bytes\n"
" untracked: %lu bytes\n"
" poisoned: %lu bytes\n"
" low offset: %lu bytes\n",
task_stack_base + THREAD_SIZE - task_stack_high,
task_stack_high - current_sp,
task_stack_high - lowest_sp,
task_stack_high - untracked_high,
untracked_high - poison_high,
poison_high - task_stack_low,
task_stack_low - task_stack_base);
if (test_failed) {
pr_err("FAIL: the thread stack is NOT properly erased!\n");
pr_expected_config(CONFIG_GCC_PLUGIN_STACKLEAK);
} else {
pr_info("OK: the rest of the thread stack is properly erased\n");
}
}
void lkdtm_STACKLEAK_ERASING(void)
{
unsigned long flags;
local_irq_save(flags);
check_stackleak_irqoff();
local_irq_restore(flags);
}
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