When attaching fentry/fexit/fmod_ret/lsm to a function located in a
module without specifying the target program, the verifier tries to find
the address to attach to in kallsyms. This is always done by searching
the entire kallsyms, not respecting the module in which the function is
located.
This approach causes an incorrect attachment address to be computed if
the function to attach to is shadowed by a function of the same name
located earlier in kallsyms.
Since the attachment must contain the BTF of the program to attach to,
we may extract the module name from it (if the attach target is a
module) and search for the function address in the correct module.
Signed-off-by: Viktor Malik <vmalik@xxxxxxxxxx>
---
include/linux/btf.h | 1 +
kernel/bpf/btf.c | 5 +++++
kernel/bpf/verifier.c | 9 ++++++++-
3 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 9ed00077db6e..bdbf3eb7083d 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -187,6 +187,7 @@ u32 btf_obj_id(const struct btf *btf);
bool btf_is_kernel(const struct btf *btf);
bool btf_is_module(const struct btf *btf);
struct module *btf_try_get_module(const struct btf *btf);
+const char *btf_module_name(const struct btf *btf);
u32 btf_nr_types(const struct btf *btf);
bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,
const struct btf_member *m,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 1a59cc7ad730..211fcbb7649d 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7192,6 +7192,11 @@ bool btf_is_module(const struct btf *btf)
return btf->kernel_btf && strcmp(btf->name, "vmlinux") != 0;
}
+const char *btf_module_name(const struct btf *btf)
+{
+ return btf->name;
+}
+
enum {
BTF_MODULE_F_LIVE = (1 << 0),
};
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9528a066cfa5..acbe62a73559 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -16343,7 +16343,14 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
else
addr = (long) tgt_prog->aux->func[subprog]->bpf_func;
} else {
- addr = kallsyms_lookup_name(tname);
+ if (btf_is_module(btf)) {
+ char tmodname[MODULE_NAME_LEN + KSYM_NAME_LEN + 1];
+ snprintf(tmodname, sizeof(tmodname), "%s:%s",
+ btf_module_name(btf), tname);
+ addr = module_kallsyms_lookup_name(tmodname);
+ }
+ else
+ addr = kallsyms_lookup_name(tname);
if (!addr) {
bpf_log(log,
"The address of function %s cannot be found\n",
--
2.38.1
