On Thu, Nov 26, 2020 at 05:57:47PM +0100, Florent Revest wrote:
> This helper exposes the kallsyms_lookup function to eBPF tracing
> programs. This can be used to retrieve the name of the symbol at an
> address. For example, when hooking into nf_register_net_hook, one can
> audit the name of the registered netfilter hook and potentially also
> the name of the module in which the symbol is located.
>
> Signed-off-by: Florent Revest <rev...@google.com>
> ---
> include/uapi/linux/bpf.h | 16 +++++++++++++
> kernel/trace/bpf_trace.c | 41 ++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 16 +++++++++++++
> 3 files changed, 73 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c3458ec1f30a..670998635eac 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3817,6 +3817,21 @@ union bpf_attr {
> * The **hash_algo** is returned on success,
> * **-EOPNOTSUP** if IMA is disabled or **-EINVAL** if
> * invalid arguments are passed.
> + *
> + * long bpf_kallsyms_lookup(u64 address, char *symbol, u32 symbol_size, char
> *module, u32 module_size)
> + * Description
> + * Uses kallsyms to write the name of the symbol at *address*
> + * into *symbol* of size *symbol_sz*. This is guaranteed to be
> + * zero terminated.
> + * If the symbol is in a module, up to *module_size* bytes of
> + * the module name is written in *module*. This is also
> + * guaranteed to be zero-terminated. Note: a module name
> + * is always shorter than 64 bytes.
> + * Return
> + * On success, the strictly positive length of the full symbol
> + * name, If this is greater than *symbol_size*, the written
> + * symbol is truncated.
> + * On error, a negative value.
Looks like debug-only helper.
I cannot think of a way to use in production code.
What program suppose to do with that string?
Do string compare? BPF side doesn't have a good way to do string manipulations.
If you really need to print a symbolic name for a given address
I'd rather extend bpf_trace_printk() to support %pS
