Commit 5bbaf9d1 authored by Sami Tolvanen's avatar Sami Tolvanen Committed by Will Deacon
Browse files

scs: Add support for stack usage debugging 



Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. When enabled,
also prints out the highest shadow stack usage per process.

Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarWill Deacon <will@kernel.org>
[will: rewrote most of scs_check_usage()]
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 628d06a4

kernel/scs.c

+29 −1
Original line number Diff line number Diff line
@@ -63,10 +63,37 @@ int scs_prepare(struct task_struct *tsk, int node) 
	task_scs(tsk) = s;

	task_scs_offset(tsk) = 0;

	scs_account(tsk, 1);



	return 0;

}



static void scs_check_usage(struct task_struct *tsk)

{

	static unsigned long highest;



	unsigned long *p, prev, curr = highest, used = 0;



	if (!IS_ENABLED(CONFIG_DEBUG_STACK_USAGE))

		return;



	for (p = task_scs(tsk); p < __scs_magic(tsk); ++p) {

		if (!READ_ONCE_NOCHECK(*p))

			break;

		used++;

	}



	while (used > curr) {

		prev = cmpxchg_relaxed(&highest, curr, used);



		if (prev == curr) {

			pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",

				tsk->comm, task_pid_nr(tsk), used);

			break;

		}



		curr = prev;

	}

}



void scs_release(struct task_struct *tsk)

{

	void *s = task_scs(tsk);
@@ -75,6 +102,7 @@ void scs_release(struct task_struct *tsk) 
		return;



	WARN(scs_corrupted(tsk), "corrupted shadow stack detected when freeing task\n");

	scs_check_usage(tsk);

	scs_account(tsk, -1);

	scs_free(s);

}