On 30/04/2025 17:46, Tao Chen wrote:
> If kernel function optimized by the compiler, the function name in
> kallsyms will have suffix like ".isra.0" or others. And fentry uses
> function name from BTF to find the function address in kallsyms, in this
> situation, it will fail due to the inconsistency of function names.
> If so, try to use the function address passed from the user.
>
> Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx>
> ---
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 1 +
> kernel/bpf/syscall.c | 1 +
> kernel/bpf/verifier.c | 9 +++++++++
> 4 files changed, 12 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 3f0cc89c06..fd53d1817f 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1626,6 +1626,7 @@ struct bpf_prog_aux {
> struct work_struct work;
> struct rcu_head rcu;
> };
> + u64 fentry_func;
> };
>
> struct bpf_prog {
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 07ee73cdf9..7016e47a70 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1577,6 +1577,7 @@ union bpf_attr {
> * If provided, prog_flags should have BPF_F_TOKEN_FD flag set.
> */
> __s32 prog_token_fd;
> + __aligned_u64 fentry_func;
since it can be used for fentry/fexit (I think from below?) might be
clearer to call it attach_func_addr or similar.
> /* The fd_array_cnt can be used to pass the length of the
> * fd_array array. In this case all the [map] file descriptors
> * passed in this array will be bound to the program, even if
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 9794446bc8..6c1e3572cc 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2892,6 +2892,7 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
> prog->sleepable = !!(attr->prog_flags & BPF_F_SLEEPABLE);
> prog->aux->attach_btf = attach_btf;
> prog->aux->attach_btf_id = attr->attach_btf_id;
> + prog->aux->fentry_func = attr->fentry_func;
> prog->aux->dst_prog = dst_prog;
> prog->aux->dev_bound = !!attr->prog_ifindex;
> prog->aux->xdp_has_frags = attr->prog_flags & BPF_F_XDP_HAS_FRAGS;
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 54c6953a8b..507c281ddc 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -23304,6 +23304,15 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
> } else {
> addr = kallsyms_lookup_name(tname);
> }
> +
> + if (!addr && (prog->expected_attach_type == BPF_TRACE_FENTRY ||
> + prog->expected_attach_type == BPF_TRACE_FEXIT)) {
> + fname = kallsyms_lookup((unsigned long)prog->aux->fentry_func,
> + NULL, NULL, NULL, trace_symbol);
> + if (fname)
> + addr = (long)prog->aux->fentry_func;
We should do some validation that the fname we get back matches the BTF
func name prefix (fname "foo.isra.0" matches "foo") I think?
> + }
> +
> if (!addr) {
> module_put(mod);
> bpf_log(log,
