Patch 4/5 is from arm64’s KPROBES_ON_FTRACE,  I think which is needed by
all RISC with both KPROBES_ON_FTRACE and -fpatchable-function-entry.

But since V7, no further patches are released, what protocol should I follow if
I need these two patches?

On Mar 26, 2021, at 3:44 AM, Steven Rostedt [off-list ref] wrote:

On Sat, 13 Mar 2021 14:41:47 +0800
Huang Pei [off-list ref] wrote:

quoted

From: Jisheng Zhang <redacted>

Looks like this was sent before, but was missing the proper authorship
(which is not Jisheng).

  https://lore.kernel.org/linux-arm-kernel/20191225173219.4f9db436@xhacker.debian/ (local)

-- Steve

quoted

Ftrace location could include more than a single instruction in case
of some architectures (powerpc64, for now). In this case, kprobe is
permitted on any of those instructions, and uses ftrace infrastructure
for functioning.

However, [dis]arm_kprobe_ftrace() uses the kprobe address when setting
up ftrace filter IP. This won't work if the address points to any
instruction apart from the one that has a branch to _mcount(). To
resolve this, have [dis]arm_kprobe_ftrace() use ftrace_function() to
identify the filter IP.

Signed-off-by: Naveen N. Rao <redacted>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
---
kernel/kprobes.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 41fdbb7953c6..66ee28b071c2 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c

@@ -1045,9 +1045,10 @@ static int prepare_kprobe(struct kprobe *p)

static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
			       int *cnt)
{
+	unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
	int ret = 0;

-	ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 0, 0);
+	ret = ftrace_set_filter_ip(ops, ftrace_ip, 0, 0);
	if (ret) {
		pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
			 p->addr, ret);

@@ -1070,7 +1071,7 @@ static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,

	 * At this point, sinec ops is not registered, we should be sefe from
	 * registering empty filter.
	 */
-	ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
+	ftrace_set_filter_ip(ops, ftrace_ip, 1, 0);
	return ret;
}

@@ -1087,6 +1088,7 @@ static int arm_kprobe_ftrace(struct kprobe *p)

static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
				  int *cnt)
{
+	unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
	int ret = 0;

	if (*cnt == 1) {

@@ -1097,7 +1099,7 @@ static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,

	(*cnt)--;

-	ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
+	ret = ftrace_set_filter_ip(ops, ftrace_ip, 1, 0);
	WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
		  p->addr, ret);
	return ret;

Huang Pei
huangpei@loongson.cn