Re: [PATCH bpf-next v2 1/2] bpf: Fix abuse of kprobe_write_ctx via freplace

[Leon Hwang]

On 2026/3/30 17:28, Jiri Olsa wrote:
> On Thu, Mar 26, 2026 at 10:17:17PM +0800, Leon Hwang wrote:
[...]
>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> index 51ade3cde8bb..1dd2ea076d8b 100644
>> --- a/kernel/bpf/syscall.c
>> +++ b/kernel/bpf/syscall.c
>> @@ -3733,6 +3733,11 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
>>  		tr = prog->aux->dst_trampoline;
>>  		tgt_prog = prog->aux->dst_prog;
>>  	}
> 
> could you please put some comment in here explaining the check, with that
> 

Sure, will add such comment:

	/*
	 * It is to prevent modifying struct pt_regs via kprobe_write_ctx=true
	 * freplace prog. Without this check, kprobe_write_ctx=true freplace
	 * prog is allowed to attach to kprobe_write_ctx=false kprobe prog, and
	 * then modify the registers of the kprobe prog's target kernel
	 * function.
	 *
	 * This also blocks the combination of uprobe+freplace, because it is
	 * unable to recognize the use of the tgt_prog as an uprobe or a kprobe
	 * by tgt_prog itself. At attach time, uprobe/kprobe is recognized by
	 * the target perf event flags in __perf_event_set_bpf_prog().
	 */

> Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> 

Thanks for your review.

Thanks,
Leon