On Wed, Jul 23, 2025 at 10:20:43AM +0800, chenyuan_fl@xxxxxxx wrote:
> From: Yuan Chen <chenyuan@xxxxxxxxxx>
>
> Adjust symbol matching logic to account for Control-flow Enforcement
> Technology (CET) on x86_64 systems. CET prefixes functions with
> a 4-byte 'endbr' instruction, shifting the actual hook entry point to
> symbol + 4.
>
> Changed in PATCH v4:
> * Refactor repeated code into a function.
> * Add detection for the x86 architecture.
>
> Changed int PATH v5:
> * Remove detection for the x86 architecture.
>
> Signed-off-by: Yuan Chen <chenyuan@xxxxxxxxxx>
> ---
> tools/bpf/bpftool/link.c | 26 ++++++++++++++++++++++++--
> 1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
> index a773e05d5ade..288bf9a032a5 100644
> --- a/tools/bpf/bpftool/link.c
> +++ b/tools/bpf/bpftool/link.c
> @@ -282,6 +282,28 @@ get_addr_cookie_array(__u64 *addrs, __u64 *cookies, __u32 count)
> return data;
> }
>
> +static bool
> +symbol_matches_target(__u64 sym_addr, __u64 target_addr)
> +{
> + if (sym_addr == target_addr)
> + return true;
> +
> +#if defined(__x86_64__)
> + /*
> + * On x86_64 architectures with CET (Control-flow Enforcement Technology),
> + * function entry points have a 4-byte 'endbr' instruction prefix.
> + * This causes kprobe hooks to target the address *after* 'endbr'
> + * (symbol address + 4), preserving the CET instruction.
> + * Here we check if the symbol address matches the hook target address
> + * minus 4, indicating a CET-enabled function entry point.
> + */
> + if (sym_addr == target_addr - 4)
> + return true;
> +#endif
looks good.. perhaps it might be too much, but should we try to read
CONFIG_X86_KERNEL_IBT value and do the check based on that? there's
already some code reading options in probe_kernel_image_config
jirka
> +
> + return false;
> +}
> +
> static void
> show_kprobe_multi_json(struct bpf_link_info *info, json_writer_t *wtr)
> {
> @@ -307,7 +329,7 @@ show_kprobe_multi_json(struct bpf_link_info *info, json_writer_t *wtr)
> goto error;
>
> for (i = 0; i < dd.sym_count; i++) {
> - if (dd.sym_mapping[i].address != data[j].addr)
> + if (!symbol_matches_target(dd.sym_mapping[i].address, data[j].addr))
> continue;
> jsonw_start_object(json_wtr);
> jsonw_uint_field(json_wtr, "addr", dd.sym_mapping[i].address);
> @@ -744,7 +766,7 @@ static void show_kprobe_multi_plain(struct bpf_link_info *info)
>
> printf("\n\t%-16s %-16s %s", "addr", "cookie", "func [module]");
> for (i = 0; i < dd.sym_count; i++) {
> - if (dd.sym_mapping[i].address != data[j].addr)
> + if (!symbol_matches_target(dd.sym_mapping[i].address, data[j].addr))
> continue;
> printf("\n\t%016lx %-16llx %s",
> dd.sym_mapping[i].address, data[j].cookie, dd.sym_mapping[i].name);
> --
> 2.25.1
>
>
