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SubjectRe: [PATCH 6/7] kprobes/ftrace: Use ftrace_location() when [dis]arming probes
On Tue, 18 Jun 2019 20:17:05 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> 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.

This looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you!

>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> kernel/kprobes.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 445337c107e0..282ee704e2d8 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -978,10 +978,10 @@ static int prepare_kprobe(struct kprobe *p)
> /* Caller must lock kprobe_mutex */
> static int arm_kprobe_ftrace(struct kprobe *p)
> {
> + unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
> int ret = 0;
>
> - ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
> - (unsigned long)p->addr, 0, 0);
> + ret = ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 0, 0);
> if (ret) {
> pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
> p->addr, ret);
> @@ -1005,13 +1005,14 @@ static int arm_kprobe_ftrace(struct kprobe *p)
> * non-empty filter_hash for IPMODIFY ops, we're safe from an accidental
> * empty filter_hash which would undesirably trace all functions.
> */
> - ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0);
> + ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 1, 0);
> return ret;
> }
>
> /* Caller must lock kprobe_mutex */
> static int disarm_kprobe_ftrace(struct kprobe *p)
> {
> + unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
> int ret = 0;
>
> if (kprobe_ftrace_enabled == 1) {
> @@ -1022,8 +1023,7 @@ static int disarm_kprobe_ftrace(struct kprobe *p)
>
> kprobe_ftrace_enabled--;
>
> - ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
> - (unsigned long)p->addr, 1, 0);
> + ret = ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 1, 0);
> WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
> p->addr, ret);
> return ret;
> --
> 2.22.0
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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