path: root/arch
diff options
authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2015-01-12 12:12:03 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-01-27 07:52:32 -0800
commit1bd60326bf850ad56f000c0a66e00c2d3f692ad8 (patch)
treeeb004ef09c99614c74f7b8223e8c0f0237262aba /arch
parent381a4fec046bebb460cb8d1ec8c4e01a7de9dce3 (diff)
ftrace/jprobes/x86: Fix conflict between jprobes and function graph tracing
commit 237d28db036e411f22c03cfd5b0f6dc2aa9bf3bc upstream. If the function graph tracer traces a jprobe callback, the system will crash. This can easily be demonstrated by compiling the jprobe sample module that is in the kernel tree, loading it and running the function graph tracer. # modprobe jprobe_example.ko # echo function_graph > /sys/kernel/debug/tracing/current_tracer # ls The first two commands end up in a nice crash after the first fork. (do_fork has a jprobe attached to it, so "ls" just triggers that fork) The problem is caused by the jprobe_return() that all jprobe callbacks must end with. The way jprobes works is that the function a jprobe is attached to has a breakpoint placed at the start of it (or it uses ftrace if fentry is supported). The breakpoint handler (or ftrace callback) will copy the stack frame and change the ip address to return to the jprobe handler instead of the function. The jprobe handler must end with jprobe_return() which swaps the stack and does an int3 (breakpoint). This breakpoint handler will then put back the saved stack frame, simulate the instruction at the beginning of the function it added a breakpoint to, and then continue on. For function tracing to work, it hijakes the return address from the stack frame, and replaces it with a hook function that will trace the end of the call. This hook function will restore the return address of the function call. If the function tracer traces the jprobe handler, the hook function for that handler will not be called, and its saved return address will be used for the next function. This will result in a kernel crash. To solve this, pause function tracing before the jprobe handler is called and unpause it before it returns back to the function it probed. Some other updates: Used a variable "saved_sp" to hold kcb->jprobe_saved_sp. This makes the code look a bit cleaner and easier to understand (various tries to fix this bug required this change). Note, if fentry is being used, jprobes will change the ip address before the function graph tracer runs and it will not be able to trace the function that the jprobe is probing. Link: http://lkml.kernel.org/r/20150114154329.552437962@goodmis.org Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
1 files changed, 15 insertions, 5 deletions
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 211bce445522..0c6c07cea3f7 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1017,6 +1017,15 @@ int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
regs->flags &= ~X86_EFLAGS_IF;
regs->ip = (unsigned long)(jp->entry);
+ /*
+ * jprobes use jprobe_return() which skips the normal return
+ * path of the function, and this messes up the accounting of the
+ * function graph tracer to get messed up.
+ *
+ * Pause function graph tracing while performing the jprobe function.
+ */
+ pause_graph_tracing();
return 1;
@@ -1042,24 +1051,25 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
u8 *addr = (u8 *) (regs->ip - 1);
struct jprobe *jp = container_of(p, struct jprobe, kp);
+ void *saved_sp = kcb->jprobe_saved_sp;
if ((addr > (u8 *) jprobe_return) &&
(addr < (u8 *) jprobe_return_end)) {
- if (stack_addr(regs) != kcb->jprobe_saved_sp) {
+ if (stack_addr(regs) != saved_sp) {
struct pt_regs *saved_regs = &kcb->jprobe_saved_regs;
"current sp %p does not match saved sp %p\n",
- stack_addr(regs), kcb->jprobe_saved_sp);
+ stack_addr(regs), saved_sp);
printk(KERN_ERR "Saved registers for jprobe %p\n", jp);
printk(KERN_ERR "Current registers\n");
+ /* It's OK to start function graph tracing again */
+ unpause_graph_tracing();
*regs = kcb->jprobe_saved_regs;
- memcpy((kprobe_opcode_t *)(kcb->jprobe_saved_sp),
- kcb->jprobes_stack,
- MIN_STACK_SIZE(kcb->jprobe_saved_sp));
+ memcpy(saved_sp, kcb->jprobes_stack, MIN_STACK_SIZE(saved_sp));
return 1;