bpf: Add bpf_kallsyms_lookup_name helper

This helper allows us to get the address of a kernel symbol from inside
a BPF_PROG_TYPE_SYSCALL prog (used by gen_loader), so that we can
relocate typeless ksym vars.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211028063501.2239335-2-memxor@gmail.com

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 50105e0..6deebf8 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2110,6 +2110,7 @@ extern const struct bpf_func_proto bpf_for_each_map_elem_proto;
 extern const struct bpf_func_proto bpf_btf_find_by_name_kind_proto;
 extern const struct bpf_func_proto bpf_sk_setsockopt_proto;
 extern const struct bpf_func_proto bpf_sk_getsockopt_proto;
+extern const struct bpf_func_proto bpf_kallsyms_lookup_name_proto;
 
 const struct bpf_func_proto *tracing_prog_func_proto(
   enum bpf_func_id func_id, const struct bpf_prog *prog);

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8bead4a..bd0c9f0 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4923,6 +4923,21 @@ union bpf_attr {
  *             Dynamically cast a *sk* pointer to a *unix_sock* pointer.
  *     Return
  *             *sk* if casting is valid, or **NULL** otherwise.
+ *
+ * long bpf_kallsyms_lookup_name(const char *name, int name_sz, int flags, u64 *res)
+ *     Description
+ *             Get the address of a kernel symbol, returned in *res*. *res* is
+ *             set to 0 if the symbol is not found.
+ *     Return
+ *             On success, zero. On error, a negative value.
+ *
+ *             **-EINVAL** if *flags* is not zero.
+ *
+ *             **-EINVAL** if string *name* is not the same size as *name_sz*.
+ *
+ *             **-ENOENT** if symbol is not found.
+ *
+ *             **-EPERM** if caller does not have permission to obtain kernel address.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5104,6 +5119,7 @@ union bpf_attr {
        FN(get_branch_snapshot),        \
        FN(trace_vprintk),              \
        FN(skc_to_unix_sock),           \
+       FN(kallsyms_lookup_name),       \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f7c2c63..e12a217 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4781,6 +4781,31 @@ static const struct bpf_func_proto bpf_sys_close_proto = {
        .arg1_type      = ARG_ANYTHING,
 };
 
+BPF_CALL_4(bpf_kallsyms_lookup_name, const char *, name, int, name_sz, int, flags, u64 *, res)
+{
+       if (flags)
+               return -EINVAL;
+
+       if (name_sz <= 1 || name[name_sz - 1])
+               return -EINVAL;
+
+       if (!bpf_dump_raw_ok(current_cred()))
+               return -EPERM;
+
+       *res = kallsyms_lookup_name(name);
+       return *res ? 0 : -ENOENT;
+}
+
+const struct bpf_func_proto bpf_kallsyms_lookup_name_proto = {
+       .func           = bpf_kallsyms_lookup_name,
+       .gpl_only       = false,
+       .ret_type       = RET_INTEGER,
+       .arg1_type      = ARG_PTR_TO_MEM,
+       .arg2_type      = ARG_CONST_SIZE,
+       .arg3_type      = ARG_ANYTHING,
+       .arg4_type      = ARG_PTR_TO_LONG,
+};
+
 static const struct bpf_func_proto *
 syscall_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -4791,6 +4816,8 @@ syscall_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
                return &bpf_btf_find_by_name_kind_proto;
        case BPF_FUNC_sys_close:
                return &bpf_sys_close_proto;
+       case BPF_FUNC_kallsyms_lookup_name:
+               return &bpf_kallsyms_lookup_name_proto;
        default:
                return tracing_prog_func_proto(func_id, prog);
        }

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 8bead4a..bd0c9f0 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4923,6 +4923,21 @@ union bpf_attr {
  *             Dynamically cast a *sk* pointer to a *unix_sock* pointer.
  *     Return
  *             *sk* if casting is valid, or **NULL** otherwise.
+ *
+ * long bpf_kallsyms_lookup_name(const char *name, int name_sz, int flags, u64 *res)
+ *     Description
+ *             Get the address of a kernel symbol, returned in *res*. *res* is
+ *             set to 0 if the symbol is not found.
+ *     Return
+ *             On success, zero. On error, a negative value.
+ *
+ *             **-EINVAL** if *flags* is not zero.
+ *
+ *             **-EINVAL** if string *name* is not the same size as *name_sz*.
+ *
+ *             **-ENOENT** if symbol is not found.
+ *
+ *             **-EPERM** if caller does not have permission to obtain kernel address.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5104,6 +5119,7 @@ union bpf_attr {
        FN(get_branch_snapshot),        \
        FN(trace_vprintk),              \
        FN(skc_to_unix_sock),           \
+       FN(kallsyms_lookup_name),       \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper