powerpc/jprobes: Validate break handler invocation as being due to a jprobe_return()

Fix a circa 2005 FIXME by implementing a check to ensure that we
actually got into the jprobe break handler() due to the trap in
jprobe_return().

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 48a8161..a14c618 100644 (file)
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -639,24 +639,22 @@ NOKPROBE_SYMBOL(setjmp_pre_handler);
 
 void __used jprobe_return(void)
 {
-       asm volatile("trap" ::: "memory");
+       asm volatile("jprobe_return_trap:\n"
+                    "trap\n"
+                    ::: "memory");
 }
 NOKPROBE_SYMBOL(jprobe_return);
 
-static void __used jprobe_return_end(void)
-{
-}
-NOKPROBE_SYMBOL(jprobe_return_end);
-
 int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 {
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 
-       /*
-        * FIXME - we should ideally be validating that we got here 'cos
-        * of the "trap" in jprobe_return() above, before restoring the
-        * saved regs...
-        */
+       if (regs->nip != ppc_kallsyms_lookup_name("jprobe_return_trap")) {
+               pr_debug("longjmp_break_handler NIP (0x%lx) does not match jprobe_return_trap (0x%lx)\n",
+                               regs->nip, ppc_kallsyms_lookup_name("jprobe_return_trap"));
+               return 0;
+       }
+
        memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
        /* It's OK to start function graph tracing again */
        unpause_graph_tracing();