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Subject[PATCH bpf-next v1 04/13] bpf: lsm: Allow btf_id based attachment for LSM hooks
Date
From: KP Singh <kpsingh@google.com>

Refactor and re-use most of the logic for BPF_PROG_TYPE_TRACING with a few
changes.

- The LSM hook BTF types are prefixed with "lsm_btf_"
- These types do not need the first (void *) pointer argument. The verifier
only looks for this argument if prod->aux->attach_btf_trace is set.

Signed-off-by: KP Singh <kpsingh@google.com>
---
kernel/bpf/syscall.c | 1 +
kernel/bpf/verifier.c | 83 ++++++++++++++++++++++++++++++++++++++++---
2 files changed, 80 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 5a773fc6f9f5..4fcaf6042c07 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1642,6 +1642,7 @@ bpf_prog_load_check_attach(enum bpf_prog_type prog_type,
{
switch (prog_type) {
case BPF_PROG_TYPE_TRACING:
+ case BPF_PROG_TYPE_LSM:
if (btf_id > BTF_MAX_TYPE)
return -EINVAL;
break;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a0482e1c4a77..0d1231d9c1ef 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9504,7 +9504,71 @@ static void print_verification_stats(struct bpf_verifier_env *env)
env->peak_states, env->longest_mark_read_walk);
}

-static int check_attach_btf_id(struct bpf_verifier_env *env)
+/*
+ * LSM hooks have a typedef associated with them. The BTF information for this
+ * type is used by the verifier to validate memory accesses made by the
+ * attached information.
+ *
+ * For example the:
+ *
+ * int bprm_check_security(struct linux_binprm *brpm)
+ *
+ * has the following typedef:
+ *
+ * typedef int (*lsm_btf_bprm_check_security)(struct linux_binprm *bprm);
+ */
+#define BTF_LSM_PREFIX "lsm_btf_"
+
+static inline int check_attach_btf_id_lsm(struct bpf_verifier_env *env)
+{
+ struct bpf_prog *prog = env->prog;
+ u32 btf_id = prog->aux->attach_btf_id;
+ const struct btf_type *t;
+ const char *tname;
+
+ if (!btf_id) {
+ verbose(env, "LSM programs must provide btf_id\n");
+ return -EINVAL;
+ }
+
+ t = btf_type_by_id(btf_vmlinux, btf_id);
+ if (!t) {
+ verbose(env, "attach_btf_id %u is invalid\n", btf_id);
+ return -EINVAL;
+ }
+
+ tname = btf_name_by_offset(btf_vmlinux, t->name_off);
+ if (!tname) {
+ verbose(env, "attach_btf_id %u doesn't have a name\n", btf_id);
+ return -EINVAL;
+ }
+
+ if (!btf_type_is_typedef(t)) {
+ verbose(env, "attach_btf_id %u is not a typedef\n", btf_id);
+ return -EINVAL;
+ }
+ if (strncmp(BTF_LSM_PREFIX, tname, sizeof(BTF_LSM_PREFIX) - 1)) {
+ verbose(env, "attach_btf_id %u points to wrong type name %s\n",
+ btf_id, tname);
+ return -EINVAL;
+ }
+
+ t = btf_type_by_id(btf_vmlinux, t->type);
+ /* should never happen in valid vmlinux build */
+ if (!btf_type_is_ptr(t))
+ return -EINVAL;
+ t = btf_type_by_id(btf_vmlinux, t->type);
+ /* should never happen in valid vmlinux build */
+ if (!btf_type_is_func_proto(t))
+ return -EINVAL;
+
+ tname += sizeof(BTF_LSM_PREFIX) - 1;
+ prog->aux->attach_func_name = tname;
+ prog->aux->attach_func_proto = t;
+ return 0;
+}
+
+static int check_attach_btf_id_tracing(struct bpf_verifier_env *env)
{
struct bpf_prog *prog = env->prog;
struct bpf_prog *tgt_prog = prog->aux->linked_prog;
@@ -9519,9 +9583,6 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
long addr;
u64 key;

- if (prog->type != BPF_PROG_TYPE_TRACING)
- return 0;
-
if (!btf_id) {
verbose(env, "Tracing programs must provide btf_id\n");
return -EINVAL;
@@ -9659,6 +9720,20 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
}
}

+static int check_attach_btf_id(struct bpf_verifier_env *env)
+{
+ struct bpf_prog *prog = env->prog;
+
+ switch (prog->type) {
+ case BPF_PROG_TYPE_TRACING:
+ return check_attach_btf_id_tracing(env);
+ case BPF_PROG_TYPE_LSM:
+ return check_attach_btf_id_lsm(env);
+ default:
+ return 0;
+ }
+}
+
int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
union bpf_attr __user *uattr)
{
--
2.20.1
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