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.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3981,6 +3996,7 @@ union bpf_attr {
FN(bprm_opts_set), \
FN(ktime_get_coarse_ns), \
FN(ima_inode_hash), \
+ FN(kallsyms_lookup), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d255bc9b2bfa..9d86e20c2b13 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -17,6 +17,7 @@
#include <linux/error-injection.h>
#include <linux/btf_ids.h>
#include <linux/bpf_lsm.h>
+#include <linux/kallsyms.h>
#include <net/bpf_sk_storage.h>
@@ -1260,6 +1261,44 @@ const struct bpf_func_proto bpf_snprintf_btf_proto = {
.arg5_type = ARG_ANYTHING,
};
+BPF_CALL_5(bpf_kallsyms_lookup, u64, address, char *, symbol, u32, symbol_size,
+ char *, module, u32, module_size)
+{
+ char buffer[KSYM_SYMBOL_LEN];
+ unsigned long offset, size;
+ const char *name;
+ char *modname;
+ long ret;
+
+ name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
+ if (!name)
+ return -EINVAL;
+
+ ret = strlen(name) + 1;
+ if (symbol_size) {
+ strncpy(symbol, name, symbol_size);
+ symbol[symbol_size - 1] = '\0';
+ }
+
+ if (modname && module_size) {
+ strncpy(module, modname, module_size);
+ module[module_size - 1] = '\0';
+ }
+
+ return ret;
+}
+
+const struct bpf_func_proto bpf_kallsyms_lookup_proto = {
+ .func = bpf_kallsyms_lookup,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_ANYTHING,
+ .arg2_type = ARG_PTR_TO_MEM,
+ .arg3_type = ARG_CONST_SIZE,
+ .arg4_type = ARG_PTR_TO_MEM,
+ .arg5_type = ARG_CONST_SIZE,
+};
+
const struct bpf_func_proto *
bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
{
@@ -1356,6 +1395,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const
struct bpf_prog *prog)
return &bpf_per_cpu_ptr_proto;
case BPF_FUNC_bpf_this_cpu_ptr:
return &bpf_this_cpu_ptr_proto;
+ case BPF_FUNC_kallsyms_lookup:
+ return &bpf_kallsyms_lookup_proto;
default:
return NULL;
}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c3458ec1f30a..670998635eac 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/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.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3981,6 +3996,7 @@ union bpf_attr {
FN(bprm_opts_set), \
FN(ktime_get_coarse_ns), \
FN(ima_inode_hash), \
+ FN(kallsyms_lookup), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.29.2.454.gaff20da3a2-goog
