ARM: kprobes: Make a frame pointer on __kretprobe_trampoline

Currently kretprobe on ARM just fills r0-r11 of pt_regs, but
that is not enough for the stacktrace. Moreover, from the user
kretprobe handler, stacktrace needs a frame pointer on the
__kretprobe_trampoline.

This adds a frame pointer on __kretprobe_trampoline for both gcc
and clang case. Those have different frame pointer so we need
different but similar stack on pt_regs.

Gcc makes the frame pointer (fp) to point the 'pc' address of
the {fp, ip (=sp), lr, pc}, this means {r11, r13, r14, r15}.
Thus if we save the r11 (fp) on pt_regs->r12, we can make this
set on the end of pt_regs.

On the other hand, Clang makes the frame pointer to point the
'fp' address of {fp, lr} on stack. Since the next to the
pt_regs->lr is pt_regs->sp, I reused the pair of pt_regs->fp
and pt_regs->ip.
So this stores the 'lr' on pt_regs->ip and make the fp to point
pt_regs->fp.

For both cases, saves __kretprobe_trampoline address to
pt_regs->lr, so that the stack tracer can identify this frame
pointer has been made by the __kretprobe_trampoline.

Note that if the CONFIG_FRAME_POINTER is not set, this keeps
fp as is.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index 95f23b47ba276d9d4248cfcb50b6fb6c9cf78f5d..4848404ba51b34ea2cbcab9b4530b6010e8894f6 100644 (file)
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -368,16 +368,36 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 /*
  * When a retprobed function returns, trampoline_handler() is called,
  * calling the kretprobe's handler. We construct a struct pt_regs to
- * give a view of registers r0-r11 to the user return-handler.  This is
- * not a complete pt_regs structure, but that should be plenty sufficient
- * for kretprobe handlers which should normally be interested in r0 only
- * anyway.
+ * give a view of registers r0-r11, sp, lr, and pc to the user
+ * return-handler. This is not a complete pt_regs structure, but that
+ * should be enough for stacktrace from the return handler with or
+ * without pt_regs.
  */
 void __naked __kprobes __kretprobe_trampoline(void)
 {
        __asm__ __volatile__ (
+#ifdef CONFIG_FRAME_POINTER
+               "ldr    lr, =__kretprobe_trampoline     \n\t"
+       /* __kretprobe_trampoline makes a framepointer on pt_regs. */
+#ifdef CONFIG_CC_IS_CLANG
+               "stmdb  sp, {sp, lr, pc}        \n\t"
+               "sub    sp, sp, #12             \n\t"
+               /* In clang case, pt_regs->ip = lr. */
+               "stmdb  sp!, {r0 - r11, lr}     \n\t"
+               /* fp points regs->r11 (fp) */
+               "add    fp, sp, #44             \n\t"
+#else /* !CONFIG_CC_IS_CLANG */
+               /* In gcc case, pt_regs->ip = fp. */
+               "stmdb  sp, {fp, sp, lr, pc}    \n\t"
                "sub    sp, sp, #16             \n\t"
                "stmdb  sp!, {r0 - r11}         \n\t"
+               /* fp points regs->r15 (pc) */
+               "add    fp, sp, #60             \n\t"
+#endif /* CONFIG_CC_IS_CLANG */
+#else /* !CONFIG_FRAME_POINTER */
+               "sub    sp, sp, #16             \n\t"
+               "stmdb  sp!, {r0 - r11}         \n\t"
+#endif /* CONFIG_FRAME_POINTER */
                "mov    r0, sp                  \n\t"
                "bl     trampoline_handler      \n\t"
                "mov    lr, r0                  \n\t"