Commit 7e9bf33b authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)
Browse files

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: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent b3ea5d56

arch/arm/probes/kprobes/core.c

+24 −4
Original line number Diff line number Diff line
@@ -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"