Commit f03a5093 authored by Mark Rutland's avatar Mark Rutland Committed by Kees Cook

lkdtm/stackleak: prevent unexpected stack usage

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: default avatarMark 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: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-11-mark.rutland@arm.com
parent 72b61896
...@@ -11,7 +11,20 @@ ...@@ -11,7 +11,20 @@
#include "lkdtm.h" #include "lkdtm.h"
#include <linux/stackleak.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_base = (unsigned long)task_stack_page(current);
const unsigned long task_stack_low = stackleak_task_low_bound(current); const unsigned long task_stack_low = stackleak_task_low_bound(current);
...@@ -81,3 +94,12 @@ void lkdtm_STACKLEAK_ERASING(void) ...@@ -81,3 +94,12 @@ void lkdtm_STACKLEAK_ERASING(void)
pr_info("OK: the rest of the thread stack is properly erased\n"); 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);
}
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment