Re: [PATCH bpf-next v3 3/6] bpf: Disallow !kprobe_write_ctx progs tail-calling kprobe_write_ctx progs

[Leon Hwang]

On 2026/3/12 18:46, Jiri Olsa wrote:
> On Thu, Mar 12, 2026 at 10:24:24AM +0800, Leon Hwang wrote:
>> On 12/3/26 06:45, Jiri Olsa wrote:
[...]
>>
>> 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@xxxxxxxxx/.

Thanks,
Leon