On Wed, Oct 27, 2021 at 11:35 PM Kumar Kartikeya Dwivedi
<memxor@xxxxxxxxx> wrote:
>
> This helper allows us to get the address of a kernel symbol from inside
> a BPF_PROG_TYPE_SYSCALL prog (used by gen_loader), so that we can
> relocate typeless ksym vars.
>
> Acked-by: Song Liu <songliubraving@xxxxxx>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 16 ++++++++++++++++
> kernel/bpf/syscall.c | 27 +++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 16 ++++++++++++++++
> 4 files changed, 60 insertions(+)
>
[...]
> +BPF_CALL_4(bpf_kallsyms_lookup_name, const char *, name, int, name_sz, int, flags, u64 *, res)
> +{
> + if (flags)
> + return -EINVAL;
> +
> + if (name_sz <= 1 || name[name_sz - 1])
> + return -EINVAL;
> +
> + if (!bpf_dump_raw_ok(current_cred()))
> + return -EPERM;
> +
> + *res = kallsyms_lookup_name(name);
> + return *res ? 0 : -ENOENT;
> +}
> +
> +const struct bpf_func_proto bpf_kallsyms_lookup_name_proto = {
> + .func = bpf_kallsyms_lookup_name,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_MEM,
> + .arg2_type = ARG_CONST_SIZE,
can you make it ARG_CONST_SIZE_OR_ZERO? Not because zero makes sense,
but because it removes the need to prove to the verifier that the size
(which you can get at runtime) is > 0. Just less unnecessary fussing
with preventing Clang optimizations.
> + .arg3_type = ARG_ANYTHING,
> + .arg4_type = ARG_PTR_TO_LONG,
> +};
> +
[...]
