On Thu, Jul 10, 2025 at 12:10 AM Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:
>
> For now, we lookup the address of the attach target in
> bpf_check_attach_target() with find_kallsyms_symbol_value or
> kallsyms_lookup_name, which is not accurate in some cases.
>
> For example, we want to attach to the target "t_next", but there are
> multiple symbols with the name "t_next" exist in the kallsyms, which makes
> the attach target ambiguous, and the attach should fail.
>
> Introduce the function bpf_lookup_attach_addr() to do the address lookup,
> which will return -EADDRNOTAVAIL when the symbol is not unique.
>
> We can do the testing with following shell:
>
> for s in $(cat /proc/kallsyms | awk '{print $3}' | sort | uniq -d)
> do
> if grep -q "^$s\$" /sys/kernel/debug/tracing/available_filter_functions
> then
> bpftrace -e "fentry:$s {printf(\"1\");}" -v
> fi
> done
>
> The script will find all the duplicated symbols in /proc/kallsyms, which
> is also in /sys/kernel/debug/tracing/available_filter_functions, and
> attach them with bpftrace.
>
> After this patch, all the attaching fail with the error:
>
> The address of function xxx cannot be found
> or
> No BTF found for xxx
>
> Signed-off-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
> ---
> v3:
> - reject all the duplicated symbols
> v2:
> - Lookup both vmlinux and modules symbols when mod is NULL, just like
> kallsyms_lookup_name().
>
> If the btf is not a modules, shouldn't we lookup on the vmlinux only?
> I'm not sure if we should keep the same logic with
> kallsyms_lookup_name().
>
> - Return the kernel symbol that don't have ftrace location if the symbols
> with ftrace location are not available
> ---
> kernel/bpf/verifier.c | 71 ++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 66 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 53007182b46b..bf4951154605 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -23476,6 +23476,67 @@ static int check_non_sleepable_error_inject(u32 btf_id)
> return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id);
> }
>
> +struct symbol_lookup_ctx {
> + const char *name;
> + unsigned long addr;
> +};
> +
> +static int symbol_callback(void *data, unsigned long addr)
> +{
> + struct symbol_lookup_ctx *ctx = data;
> +
> + if (ctx->addr)
> + return -EADDRNOTAVAIL;
#define ENOTUNIQ 76 /* Name not unique on network */
fits a bit better, no?
> + ctx->addr = addr;
> +
> + return 0;
> +}
> +
[...]
