tracing, x86: add low level support for ftrace return tracing

Impact: add infrastructure for function-return tracing

Add low level support for ftrace return tracing.

This plug-in stores return addresses on the thread_info structure of
the current task.

The index of the current return address is initialized when the task
is the first one (init) and when a process forks (the child). It is
not needed when a task does a sys_execve because after this syscall,
it still needs to return on the kernel functions it called.

Note that the code of return_to_handler has been suggested by Steven
Rostedt as almost all of the ideas of improvements in this V3.

For purpose of security, arch/x86/kernel/process_32.c is not traced
because __switch_to() changes the current task during its execution.
That could cause inconsistency in the stored return address of this
function even if I didn't have any crash after testing with tracing on
this function enabled.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 50 insertions, 0 deletions

diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index f8173ed1c97..9b6a1fa19e7 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -20,4 +20,30 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_FUNCTION_TRACER */
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+#define FTRACE_RET_STACK_SIZE 20
+
+#ifndef __ASSEMBLY__
+
+/*
+ * Stack of return addresses for functions
+ * of a thread.
+ * Used in struct thread_info
+ */
+struct ftrace_ret_stack {
+        unsigned long ret;
+        unsigned long func;
+        unsigned long long calltime;
+};
+
+/*
+ * Primary handler of a function return.
+ * It relays on ftrace_return_to_handler.
+ * Defined in entry32.S
+ */
+extern void return_to_handler(void);
+
+#endif /* __ASSEMBLY__ */
+#endif /* CONFIG_FUNCTION_RET_TRACER */
+
 #endif /* _ASM_X86_FTRACE_H */
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index e44d379faad..a71158369fd 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -20,6 +20,7 @@
 struct task_struct;
 struct exec_domain;
 #include <asm/processor.h>
+#include <asm/ftrace.h>
 
 struct thread_info {
         struct task_struct      *task;          /* main task structure */
@@ -38,8 +39,30 @@ struct thread_info {
                                                 */
         __u8                    supervisor_stack[0];
 #endif
+
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        /* Index of current stored adress in ret_stack */
+        int             curr_ret_stack;
+        /* Stack of return addresses for return function tracing */
+        struct ftrace_ret_stack ret_stack[FTRACE_RET_STACK_SIZE];
+#endif
 };
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+#define INIT_THREAD_INFO(tsk)                   \
+{                                               \
+        .task           = &tsk,                 \
+        .exec_domain    = &default_exec_domain, \
+        .flags          = 0,                    \
+        .cpu            = 0,                    \
+        .preempt_count  = 1,                    \
+        .addr_limit     = KERNEL_DS,            \
+        .restart_block = {                      \
+                .fn = do_no_restart_syscall,    \
+        },                                      \
+        .curr_ret_stack = -1,\
+}
+#else
 #define INIT_THREAD_INFO(tsk)                   \
 {                                               \
         .task           = &tsk,                 \
@@ -52,6 +75,7 @@ struct thread_info {
                 .fn = do_no_restart_syscall,    \
         },                                      \
 }
+#endif
 
 #define init_thread_info        (init_thread_union.thread_info)
 #define init_stack              (init_thread_union.stack)