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lkdtm/stackleak: prevent unexpected stack usage

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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
This commit is contained in:
Mark Rutland 2022-04-27 18:31:25 +01:00 committed by Kees Cook
parent 72b61896f2
commit f03a50938d
1 changed files with 23 additions and 1 deletions
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24
drivers/misc/lkdtm/stackleak.c
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@ -11,7 +11,20 @@
#include "lkdtm.h"
#include <linux/stackleak.h>
void lkdtm_STACKLEAK_ERASING(void)
/*
* 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);
@ -81,3 +94,12 @@ void lkdtm_STACKLEAK_ERASING(void)
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);
}