[PATCH v2 1/4] stacktrace: add interface based on shadow call stack

[andrey.konovalov@linux.dev]

From: Andrey Konovalov <andreyknvl@google.com>

Add a new interface stack_trace_save_shadow() for collecting stack traces
by copying frames from the Shadow Call Stack.

Collecting stack traces this way is significantly faster: boot time
of a defconfig build with KASAN enabled gets descreased by ~30%.

The few patches following this one add an implementation of
stack_trace_save_shadow() for arm64.

The implementation of the added interface is not meant to use
stack_trace_consume_fn to avoid making a function call for each
collected frame to further improve performance.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/Kconfig               |  6 ++++++
 include/linux/stacktrace.h | 15 +++++++++++++++
 kernel/stacktrace.c        | 21 +++++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index e12a4268c01d..207c1679c53a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1041,6 +1041,12 @@ config HAVE_RELIABLE_STACKTRACE
 	  arch_stack_walk_reliable() function which only returns a stack trace
 	  if it can guarantee the trace is reliable.
 
+config HAVE_SHADOW_STACKTRACE
+	bool
+	help
+	  If this is set, the architecture provides the arch_stack_walk_shadow()
+	  function, which collects the stack trace from the shadow call stack.
+
 config HAVE_ARCH_HASH
 	bool
 	default n
diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
index 97455880ac41..b74d1e42e157 100644
--- a/include/linux/stacktrace.h
+++ b/include/linux/stacktrace.h
@@ -60,6 +60,9 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry, void *cookie,
 
 void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
 			  const struct pt_regs *regs);
+
+int arch_stack_walk_shadow(unsigned long *store, unsigned int size,
+			   unsigned int skipnr);
 #endif /* CONFIG_ARCH_STACKWALK */
 
 #ifdef CONFIG_STACKTRACE
@@ -108,4 +111,16 @@ static inline int stack_trace_save_tsk_reliable(struct task_struct *tsk,
 }
 #endif
 
+#if defined(CONFIG_STACKTRACE) && defined(CONFIG_HAVE_SHADOW_STACKTRACE)
+int stack_trace_save_shadow(unsigned long *store, unsigned int size,
+			    unsigned int skipnr);
+#else
+static inline int stack_trace_save_shadow(unsigned long *store,
+					  unsigned int size,
+					  unsigned int skipnr)
+{
+	return -ENOSYS;
+}
+#endif
+
 #endif /* __LINUX_STACKTRACE_H */
diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 9ed5ce989415..fe305861fd55 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -237,6 +237,27 @@ unsigned int stack_trace_save_user(unsigned long *store, unsigned int size)
 }
 #endif
 
+#ifdef CONFIG_HAVE_SHADOW_STACKTRACE
+/**
+ * stack_trace_save_shadow - Save a stack trace based on shadow call stack
+ * @store:	Pointer to the storage array
+ * @size:	Size of the storage array
+ * @skipnr:	Number of entries to skip at the start of the stack trace
+ *
+ * Return: Number of trace entries stored.
+ */
+int stack_trace_save_shadow(unsigned long *store, unsigned int size,
+			    unsigned int skipnr)
+{
+	/*
+	 * Do not use stack_trace_consume_fn to avoid making a function
+	 * call for each collected frame to improve performance.
+	 * Skip + 1 frame to skip stack_trace_save_shadow.
+	 */
+	return arch_stack_walk_shadow(store, size, skipnr + 1);
+}
+#endif
+
 #else /* CONFIG_ARCH_STACKWALK */
 
 /*
-- 
2.25.1