linux-kernel - [PATCH] Revert "kprobes: Warn if optprobe handler tries to change execution path"

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Date:   Tue, 17 Oct 2017 13:48:34 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] Revert "kprobes: Warn if optprobe handler tries to change execution path"

This reverts commit e863d539614641 ("kprobes: Warn if optprobe handler
tries to change execution path").

On powerpc, we place a probe at kretprobe_trampoline to catch function
returns and with CONFIG_OPTPROBES, this probe gets optimized. This
works for us due to the way we handle the optprobe as described in
commit 762df10bad6954 ("powerpc/kprobes: Optimize kprobe
in kretprobe_trampoline()"). With the above commit, we end up with a
warning. As such, revert this change.

Reported-by: Michael Ellerman <mpe@...erman.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
Discussion here:
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1510995.html

 kernel/kprobes.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 2d28377a0e32..15fba7fe57c8 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -387,10 +387,7 @@ void opt_pre_handler(struct kprobe *p, struct pt_regs *regs)
 	list_for_each_entry_rcu(kp, &p->list, list) {
 		if (kp->pre_handler && likely(!kprobe_disabled(kp))) {
 			set_kprobe_instance(kp);
-			if (kp->pre_handler(kp, regs)) {
-				if (WARN_ON_ONCE(1))
-					pr_err("Optprobe ignores instruction pointer changing.(%pF)\n", p->addr);
-			}
+			kp->pre_handler(kp, regs);
 		}
 		reset_kprobe_instance();
 	}
-- 
2.14.2