On Thu, Jul 30, 2026 at 10:20 PM Leon Hwang <[email protected]> wrote: > > On 31/7/26 08:07, Andrii Nakryiko wrote: > > On Sat, Jul 25, 2026 at 6:27 AM Leon Hwang <[email protected]> wrote: > >> > >> When CONFIG_FUNCTION_ERROR_INJECTION is disabled, a sleepable tracing prog > >> is allowed to attach to '__x64_'-alike prefix symbols. > >> > >> It is because the verifier does not verify whether the symbol is a kernel > >> function or a bpf prog. That said, a sleepable tracing prog is allowed to > >> attach to a bpf prog target whose name has '__x64_'-alike prefix. > >> > >> For example, a sleepable fentry prog attaches to a '__x64_sys_nop' XDP > > > > we do have addr, so we should be able to distinguish between attaching > > to kernel function vs BPF program, no? > > > Yes, we can distinguish a bpf prog from a kernel function by addr. > > I'd prefer passing 'tgt_prog' to btf_id_allow_sleepable() as a simple > change. >
I don't think there is a need for new tgt_prog argument, we can just check that supplied btf is not kernel/module BTF (see btf_is_kernel()) > > > >> prog, and copies buffer from a user pointer with bpf_copy_from_user() > >> helper. After attaching the XDP prog to lo interface, the kernel BUG > >> could be triggered by 'ping -c 1 -W 1 127.0.0.1': > >> > >> [ 3.460756] BUG: sleeping function called from invalid context at > >> kernel/bpf/trampoline.c:1324 > >> > >> Fix it by disallowing sleepable tracing prog always when its target is > >> bpf prog. > > > > what happens when we freplace sleepable BPF program/subprogram with > > another sleepable BPF subprogram? And same question for sleepable > > fentry/fexit program attaching to sleepable BPF program? Is it > > something that just cannot work or we can actually allow that? > > > Currently, sleepable freplace/fentry/fexit progs are already disallowed > from attaching to bpf prog, because btf_id_allow_sleepable() returns > -EINVAL for them (except for this BUG). > > Since no one has proposed relaxing the restriction, I'd like to keep it > as-is when fixing this BUG. > > I'm not sure whether allowing it would introduce any issue. > > Thanks, > Leon > > > [...] > >
