Re: [PATCH v2 2/3] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE

From: Naveen N. Rao
Date: Tue Aug 20 2019 - 06:15:38 EST

Jisheng Zhang wrote:
For KPROBES_ON_FTRACE case, we need to adjust the kprobe's addr

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx>
kernel/kprobes.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 9873fc627d61..3fd2f68644da 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1484,15 +1484,19 @@ static inline int check_kprobe_rereg(struct kprobe *p)
int __weak arch_check_ftrace_location(struct kprobe *p)
- unsigned long ftrace_addr;
+ unsigned long ftrace_addr, addr = (unsigned long)p->addr;
- ftrace_addr = ftrace_location((unsigned long)p->addr);
+ addr = ftrace_call_adjust(addr);

Looking at the commit message for patch 3/3, it looks like you want the probe to be placed on ftrace entry by default, and this patch seems to be aimed at that.

If so, this is not the right approach. As I mentioned previously, you would want to over-ride kprobe_lookup_name(). This ensures that the address is changed only if the user provided a symbol, and not if the user wanted to probe at a very specific address. See commit 24bd909e94776 ("powerpc/kprobes: Prefer ftrace when probing function entry").

If this patch is for some other purpose, then it isn't clear from the commit log. Please provide a better explanation.

- Naveen