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>

1 files changed, 33 insertions, 0 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 9134de814c97..9a0ac85946db 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1188,6 +1188,10 @@ ENTRY(mcount)
 
         cmpl $ftrace_stub, ftrace_trace_function
         jnz trace
+#ifdef CONFIG_FUNCTION_RET_TRACER
+        cmpl $ftrace_stub, ftrace_function_return
+        jnz trace_return
+#endif
 .globl ftrace_stub
 ftrace_stub:
         ret
@@ -1206,8 +1210,37 @@ trace:
         popl %edx
         popl %ecx
         popl %eax
+        jmp ftrace_stub
 
+#ifdef CONFIG_FUNCTION_RET_TRACER
+trace_return:
+        pushl %eax
+        pushl %ecx
+        pushl %edx
+        movl 0xc(%esp), %eax
+        pushl %eax
+        lea 0x4(%ebp), %eax
+        pushl %eax
+        call prepare_ftrace_return
+        addl $8, %esp
+        popl %edx
+        popl %ecx
+        popl %eax
         jmp ftrace_stub
+
+.globl return_to_handler
+return_to_handler:
+        pushl $0
+        pushl %eax
+        pushl %ecx
+        pushl %edx
+        call ftrace_return_to_handler
+        movl %eax, 0xc(%esp)
+        popl %edx
+        popl %ecx
+        popl %eax
+        ret
+#endif /* CONFIG_FUNCTION_RET_TRACER */
 END(mcount)
 #endif /* CONFIG_DYNAMIC_FTRACE */
 #endif /* CONFIG_FUNCTION_TRACER */