On Tue, Dec 26, 2017 at 04:47:26PM +0900, Masami Hiramatsu wrote:
> Compare instruction pointer with original one on the
> stack instead using per-cpu bpf_kprobe_override flag.
>
> This patch also consolidates reset_current_kprobe() and
> preempt_enable_no_resched() blocks. Those can be done
> in one place.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> ---
> kernel/trace/bpf_trace.c | 1 -
> kernel/trace/trace_kprobe.c | 21 +++++++--------------
> 2 files changed, 7 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index d663660f8392..cefa9b0e396c 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -83,7 +83,6 @@ EXPORT_SYMBOL_GPL(trace_call_bpf);
> #ifdef CONFIG_BPF_KPROBE_OVERRIDE
> BPF_CALL_2(bpf_override_return, struct pt_regs *, regs, unsigned long, rc)
> {
> - __this_cpu_write(bpf_kprobe_override, 1);
> regs_set_return_value(regs, rc);
> arch_ftrace_kprobe_override_function(regs);
> return 0;
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 265e3e27e8dc..a7c7035963f2 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -42,8 +42,6 @@ struct trace_kprobe {
> (offsetof(struct trace_kprobe, tp.args) + \
> (sizeof(struct probe_arg) * (n)))
>
> -DEFINE_PER_CPU(int, bpf_kprobe_override);
> -
> static nokprobe_inline bool trace_kprobe_is_return(struct trace_kprobe *tk)
> {
> return tk->rp.handler != NULL;
> @@ -1204,6 +1202,7 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
> int rctx;
>
> if (bpf_prog_array_valid(call)) {
> + unsigned long orig_ip = instruction_pointer(regs);
> int ret;
>
> ret = trace_call_bpf(call, regs);
> @@ -1211,12 +1210,13 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
> /*
> * We need to check and see if we modified the pc of the
> * pt_regs, and if so clear the kprobe and return 1 so that we
> - * don't do the instruction skipping. Also reset our state so
> - * we are clean the next pass through.
> + * don't do the single stepping.
> + * The ftrace kprobe handler leaves it up to us to re-enable
> + * preemption here before returning if we've modified the ip.
> */
> - if (__this_cpu_read(bpf_kprobe_override)) {
> - __this_cpu_write(bpf_kprobe_override, 0);
> + if (orig_ip != instruction_pointer(regs)) {
> reset_current_kprobe();
> + preempt_enable_no_resched();
This is great idea.
Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>
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