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Commit 32518aee authored by Sami Tolvanen's avatar Sami Tolvanen Committed by Alistair Delva
Browse files

FROMLIST: 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.

Bug: 145210207
Change-Id: I4c085b51e1432e8d52e54126ffd8bf7b6e35b529
(am from https://lore.kernel.org/patchwork/patch/1149056/

)
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
parent 9c265248

kernel/scs.c

+39 −0
Original line number Diff line number Diff line
@@ -184,6 +184,44 @@ int scs_prepare(struct task_struct *tsk, int node) 
	return 0;

}



#ifdef CONFIG_DEBUG_STACK_USAGE

static inline unsigned long scs_used(struct task_struct *tsk)

{

	unsigned long *p = __scs_base(tsk);

	unsigned long *end = scs_magic(p);

	unsigned long s = (unsigned long)p;



	while (p < end && READ_ONCE_NOCHECK(*p))

		p++;



	return (unsigned long)p - s;

}



static void scs_check_usage(struct task_struct *tsk)

{

	static DEFINE_SPINLOCK(lock);

	static unsigned long highest;

	unsigned long used = scs_used(tsk);



	if (used <= highest)

		return;



	spin_lock(&lock);



	if (used > highest) {

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

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

		highest = used;

	}



	spin_unlock(&lock);

}

#else

static inline void scs_check_usage(struct task_struct *tsk)

{

}

#endif



bool scs_corrupted(struct task_struct *tsk)

{

	unsigned long *magic = scs_magic(__scs_base(tsk));
@@ -200,6 +238,7 @@ void scs_release(struct task_struct *tsk) 
		return;



	WARN_ON(scs_corrupted(tsk));

	scs_check_usage(tsk);



	scs_account(tsk, -1);

	task_set_scs(tsk, NULL);