linux-kernel - [PATCH 4.9 18/44] powerpc/kprobes: Pause function

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Date:   Tue, 27 Jun 2017 16:12:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 4.9 18/44] powerpc/kprobes: Pause function_graph tracing during jprobes handling

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>

commit a9f8553e935f26cb5447f67e280946b0923cd2dc upstream.

This fixes a crash when function_graph and jprobes are used together.
This is essentially commit 237d28db036e ("ftrace/jprobes/x86: Fix
conflict between jprobes and function graph tracing"), but for powerpc.

Jprobes breaks function_graph tracing since the jprobe hook needs to use
jprobe_return(), which never returns back to the hook, but instead to
the original jprobe'd function. The solution is to momentarily pause
function_graph tracing before invoking the jprobe hook and re-enable it
when returning back to the original jprobe'd function.

Fixes: 6794c78243bf ("powerpc64: port of the function graph tracer")
Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/kernel/kprobes.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -511,6 +511,15 @@ int __kprobes setjmp_pre_handler(struct
 	regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 #endif

+	/*
+	 * jprobes use jprobe_return() which skips the normal return
+	 * path of the function, and this messes up the accounting of the
+	 * function graph tracer.
+	 *
+	 * Pause function graph tracing while performing the jprobe function.
+	 */
+	pause_graph_tracing();
+
 	return 1;
 }

@@ -533,6 +542,8 @@ int __kprobes longjmp_break_handler(stru
 	 * saved regs...
 	 */
 	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
+	/* It's OK to start function graph tracing again */
+	unpause_graph_tracing();
 	preempt_enable_no_resched();
 	return 1;
 }