Commit 8111e67d authored by Mark Rutland's avatar Mark Rutland Committed by Kees Cook
Browse files

stackleak: add on/off stack variants 



The stackleak_erase() code dynamically handles being on a task stack or
another stack. In most cases, this is a fixed property of the caller,
which the caller is aware of, as an architecture might always return
using the task stack, or might always return using a trampoline stack.

This patch adds stackleak_erase_on_task_stack() and
stackleak_erase_off_task_stack() functions which callers can use to
avoid on_thread_stack() check and associated redundant work when the
calling stack is known. The existing stackleak_erase() is retained as a
safe default.

There should be no functional change as a result of this patch.

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: Kees Cook <keescook@chromium.org>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220427173128.2603085-13-mark.rutland@arm.com
parent f171d695

kernel/stackleak.c

+32 −3
Original line number Diff line number Diff line
@@ -70,7 +70,7 @@ late_initcall(stackleak_sysctls_init); 
#define skip_erasing()	false

#endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */



static __always_inline void __stackleak_erase(void)

static __always_inline void __stackleak_erase(bool on_task_stack)

{

	const unsigned long task_stack_low = stackleak_task_low_bound(current);

	const unsigned long task_stack_high = stackleak_task_high_bound(current);
@@ -96,7 +96,7 @@ static __always_inline void __stackleak_erase(void) 
	 * function has a fixed-size stack frame, and the current stack pointer

	 * doesn't change while we write poison.

	 */

	if (on_thread_stack())

	if (on_task_stack)

		erase_high = current_stack_pointer;

	else

		erase_high = task_stack_high;
@@ -110,12 +110,41 @@ static __always_inline void __stackleak_erase(void) 
	current->lowest_stack = task_stack_high;

}



/*

 * Erase and poison the portion of the task stack used since the last erase.

 * Can be called from the task stack or an entry stack when the task stack is

 * no longer in use.

 */

asmlinkage void noinstr stackleak_erase(void)

{

	if (skip_erasing())

		return;



	__stackleak_erase();

	__stackleak_erase(on_thread_stack());

}



/*

 * Erase and poison the portion of the task stack used since the last erase.

 * Can only be called from the task stack.

 */

asmlinkage void noinstr stackleak_erase_on_task_stack(void)

{

	if (skip_erasing())

		return;



	__stackleak_erase(true);

}



/*

 * Erase and poison the portion of the task stack used since the last erase.

 * Can only be called from a stack other than the task stack.

 */

asmlinkage void noinstr stackleak_erase_off_task_stack(void)

{

	if (skip_erasing())

		return;



	__stackleak_erase(false);

}



void __used __no_caller_saved_registers noinstr stackleak_track_stack(void)