On 2026/3/12 18:46, Jiri Olsa wrote:

On Thu, Mar 12, 2026 at 10:24:24AM +0800, Leon Hwang wrote:

quoted

On 12/3/26 06:45, Jiri Olsa wrote:

[...]

quoted

Actually, without this patch, when "bpf_fentry_test1" runs, the arg "a"
will be updated as 0. Thus, bpf_prog_test_run_tracing() returns -EFAULT
instead of 0.

bpf_prog_test_run_tracing()
|-->bpf_fentry_test1()
    |-->dummy_kprobe()
        |-->kprobe() /* via tail call */
            |-->regs->di = 0;
    return 1; /* instead of 2 */
return -EFAULT;

Yep, the commit log is not clear to describe this abuse problem. Will
update it.

ah right :-\ ok, I think we need to do the suggested one way check and
that should prevent kprobes having writeable ctx

Yeah, will apply strict both-ways check. See
https://lore.kernel.org/bpf/8a3c7f14-b3d1-4208-acbd-76e5db6c5320@linux.dev/ (local).

Thanks,
Leon