diff mbox series

[v12,03/12] scs: add support for stack usage debugging

Message ID 20200421021453.198187-4-samitolvanen@google.com (mailing list archive)
State New, archived
Headers show
Series add support for Clang's Shadow Call Stack | expand

Commit Message

Sami Tolvanen April 21, 2020, 2:14 a.m. UTC 
Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. When enabled,
also prints out the highest shadow stack usage per process.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 kernel/scs.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

Comments

Will Deacon April 22, 2020, 5:46 p.m. UTC | #1 
On Mon, Apr 20, 2020 at 07:14:44PM -0700, Sami Tolvanen wrote:
> Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. When enabled,
> also prints out the highest shadow stack usage per process.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> ---
>  kernel/scs.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/kernel/scs.c b/kernel/scs.c
> index 7eea2d97bd2d..147917e31adf 100644
> --- a/kernel/scs.c
> +++ b/kernel/scs.c
> @@ -68,6 +68,43 @@ int scs_prepare(struct task_struct *tsk, int node)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_DEBUG_STACK_USAGE
> +static 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 unsigned long highest;
> +	unsigned long used = __scs_used(tsk);
> +	unsigned long prev;
> +	unsigned long curr = highest;
> +
> +	while (used > curr) {
> +		prev = cmpxchg(&highest, curr, used);

I think this can be cmpxchg_relaxed(), since we don't care about ordering
here afaict.

With that:

Acked-by: Will Deacon <will@kernel.org>

Cheers,

Will
Sami Tolvanen April 22, 2020, 11:53 p.m. UTC | #2 
On Wed, Apr 22, 2020 at 06:46:02PM +0100, Will Deacon wrote:
> > +static void scs_check_usage(struct task_struct *tsk)
> > +{
> > +	static unsigned long highest;
> > +	unsigned long used = __scs_used(tsk);
> > +	unsigned long prev;
> > +	unsigned long curr = highest;
> > +
> > +	while (used > curr) {
> > +		prev = cmpxchg(&highest, curr, used);
> 
> I think this can be cmpxchg_relaxed(), since we don't care about ordering
> here afaict.

Sure, I'll change this in v13. Thanks.

Sami
diff mbox series

Patch

diff --git a/kernel/scs.c b/kernel/scs.c
index 7eea2d97bd2d..147917e31adf 100644
--- a/kernel/scs.c
+++ b/kernel/scs.c
@@ -68,6 +68,43 @@  int scs_prepare(struct task_struct *tsk, int node)
 	return 0;
 }
 
+#ifdef CONFIG_DEBUG_STACK_USAGE
+static 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 unsigned long highest;
+	unsigned long used = __scs_used(tsk);
+	unsigned long prev;
+	unsigned long curr = highest;
+
+	while (used > curr) {
+		prev = cmpxchg(&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;
+	}
+}
+#else
+static inline void scs_check_usage(struct task_struct *tsk) {}
+#endif
+
 void scs_release(struct task_struct *tsk)
 {
 	void *s;
@@ -77,6 +114,7 @@  void scs_release(struct task_struct *tsk)
 		return;
 
 	WARN_ON(scs_corrupted(tsk));
+	scs_check_usage(tsk);
 
 	scs_account(tsk, -1);
 	scs_free(s);