On Thu, 2024-04-25 at 18:28 -0600, Daniel Xu wrote:
> This commit teaches pahole to parse symbols in .BTF_ids section in
> vmlinux and discover exported kfuncs. Pahole then takes the list of
> kfuncs and injects a BTF_KIND_DECL_TAG for each kfunc.
>
> Example of encoding:
>
> $ bpftool btf dump file .tmp_vmlinux.btf | rg "DECL_TAG 'bpf_kfunc'" | wc -l
> 121
>
> $ bpftool btf dump file .tmp_vmlinux.btf | rg 56337
> [56337] FUNC 'bpf_ct_change_timeout' type_id=56336 linkage=static
> [127861] DECL_TAG 'bpf_kfunc' type_id=56337 component_idx=-1
>
> This enables downstream users and tools to dynamically discover which
> kfuncs are available on a system by parsing vmlinux or module BTF, both
> available in /sys/kernel/btf.
>
> This feature is enabled with --btf_features=decl_tag,decl_tag_kfuncs.
>
> Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> Tested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> Tested-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
> ---
I tested this patch-set on current master with Makefile.btf modified
to have --btf_features=+decl_tag_kfuncs, the tests are passing.
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
(But please fix get_func_name...)
[...]
> +static char *get_func_name(const char *sym)
> +{
> + char *func, *end;
> +
> + /* Example input: __BTF_ID__func__vfs_close__1
> + *
> + * The goal is to strip the prefix and suffix such that we only
> + * return vfs_close.
> + */
> +
> + if (!strstarts(sym, BTF_ID_FUNC_PFX))
> + return NULL;
> +
> + /* Strip prefix and handle malformed input such as __BTF_ID__func___ */
> + func = strdup(sym + sizeof(BTF_ID_FUNC_PFX) - 1);
> + if (strlen(func) < 2) {
> + free(func);
> + return NULL;
> + }
> +
> + /* Strip suffix */
> + end = strrchr(func, '_');
> + if (!end || *(end - 1) != '_') {
Sorry, I'm complaining about this silly function again...
This will do an invalid read for input like "__BTF_ID__func___a":
- 'func' would be a result of strdup("_a");
- 'end' would point to the first character of 'func';
- 'end - 1' would point outside of 'func'.
Here is a repro with valgrind report:
https://gist.github.com/eddyz87/dfd653ada6584b7b7563fbfe66355eae
> + free(func);
> + return NULL;
> + }
> + *(end - 1) = '\0';
> +
> + return func;
> +}
[...]
