f03a50938d
The lkdtm_STACKLEAK_ERASING() test is instrumentable and runs with IRQs unmasked, so it's possible for unrelated code to clobber the task stack and/or manipulate current->lowest_stack while the test is running, resulting in spurious failures. The regular stackleak erasing code is non-instrumentable and runs with IRQs masked, preventing similar issues. Make the body of the test non-instrumentable, and run it with IRQs masked, avoiding such spurious failures. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Popov <alex.popov@linux.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Kees Cook <keescook@chromium.org> Cc: Will Deacon <will@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220427173128.2603085-11-mark.rutland@arm.com
106 lines
3.5 KiB
C
106 lines
3.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* This code tests that the current task stack is properly erased (filled
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* with STACKLEAK_POISON).
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*
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* Authors:
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* Alexander Popov <alex.popov@linux.com>
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* Tycho Andersen <tycho@tycho.ws>
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*/
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#include "lkdtm.h"
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#include <linux/stackleak.h>
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/*
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* Check that stackleak tracks the lowest stack pointer and erases the stack
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* below this as expected.
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*
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* To prevent the lowest stack pointer changing during the test, IRQs are
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* masked and instrumentation of this function is disabled. We assume that the
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* compiler will create a fixed-size stack frame for this function.
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*
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* Any non-inlined function may make further use of the stack, altering the
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* lowest stack pointer and/or clobbering poison values. To avoid spurious
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* failures we must avoid printing until the end of the test or have already
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* encountered a failure condition.
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*/
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static void noinstr check_stackleak_irqoff(void)
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{
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const unsigned long task_stack_base = (unsigned long)task_stack_page(current);
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const unsigned long task_stack_low = stackleak_task_low_bound(current);
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const unsigned long task_stack_high = stackleak_task_high_bound(current);
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const unsigned long current_sp = current_stack_pointer;
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const unsigned long lowest_sp = current->lowest_stack;
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unsigned long untracked_high;
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unsigned long poison_high, poison_low;
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bool test_failed = false;
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/*
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* Depending on what has run prior to this test, the lowest recorded
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* stack pointer could be above or below the current stack pointer.
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* Start from the lowest of the two.
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*
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* Poison values are naturally-aligned unsigned longs. As the current
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* stack pointer might not be sufficiently aligned, we must align
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* downwards to find the lowest known stack pointer value. This is the
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* high boundary for a portion of the stack which may have been used
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* without being tracked, and has to be scanned for poison.
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*/
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untracked_high = min(current_sp, lowest_sp);
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untracked_high = ALIGN_DOWN(untracked_high, sizeof(unsigned long));
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/*
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* Find the top of the poison in the same way as the erasing code.
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*/
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poison_high = stackleak_find_top_of_poison(task_stack_low, untracked_high);
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/*
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* Check whether the poisoned portion of the stack (if any) consists
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* entirely of poison. This verifies the entries that
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* stackleak_find_top_of_poison() should have checked.
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*/
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poison_low = poison_high;
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while (poison_low > task_stack_low) {
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poison_low -= sizeof(unsigned long);
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if (*(unsigned long *)poison_low == STACKLEAK_POISON)
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continue;
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pr_err("FAIL: non-poison value %lu bytes below poison boundary: 0x%lx\n",
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poison_high - poison_low, *(unsigned long *)poison_low);
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test_failed = true;
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}
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pr_info("stackleak stack usage:\n"
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" high offset: %lu bytes\n"
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" current: %lu bytes\n"
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" lowest: %lu bytes\n"
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" tracked: %lu bytes\n"
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" untracked: %lu bytes\n"
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" poisoned: %lu bytes\n"
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" low offset: %lu bytes\n",
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task_stack_base + THREAD_SIZE - task_stack_high,
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task_stack_high - current_sp,
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task_stack_high - lowest_sp,
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task_stack_high - untracked_high,
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untracked_high - poison_high,
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poison_high - task_stack_low,
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task_stack_low - task_stack_base);
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if (test_failed) {
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pr_err("FAIL: the thread stack is NOT properly erased!\n");
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pr_expected_config(CONFIG_GCC_PLUGIN_STACKLEAK);
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} else {
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pr_info("OK: the rest of the thread stack is properly erased\n");
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}
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}
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void lkdtm_STACKLEAK_ERASING(void)
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{
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unsigned long flags;
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local_irq_save(flags);
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check_stackleak_irqoff();
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local_irq_restore(flags);
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}
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