[RFC bpf-next 05/11] bpf: dynamic allocation for bpf_verifier_env->subprog_info

[Eduard Zingerman <eddyz87@gmail.com>]

Follow-up patches use add_hidden_subprog() to inject inlinable kfunc
bodies into bpf program as subprograms. At the moment only one hidden
subprogram is allowed, as bpf_verifier_env->subprog_info is allocated
in advance as array of fixed size. This patch removes the limitation
by using dynamic memory allocation for this array.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 include/linux/bpf_verifier.h |  3 ++-
 kernel/bpf/verifier.c        | 29 ++++++++++++++++++++++-------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index ed4eacfd4db7..b683dc3ede4a 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -738,7 +738,7 @@ struct bpf_verifier_env {
 	struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
 	const struct bpf_line_info *prev_linfo;
 	struct bpf_verifier_log log;
-	struct bpf_subprog_info subprog_info[BPF_MAX_SUBPROGS + 2]; /* max + 2 for the fake and exception subprogs */
+	struct bpf_subprog_info *subprog_info;
 	union {
 		struct bpf_idmap idmap_scratch;
 		struct bpf_idset idset_scratch;
@@ -751,6 +751,7 @@ struct bpf_verifier_env {
 	struct backtrack_state bt;
 	struct bpf_jmp_history_entry *cur_hist_ent;
 	u32 pass_cnt; /* number of times do_check() was called */
+	u32 subprog_cap;
 	u32 subprog_cnt;
 	/* number of instructions analyzed by the verifier */
 	u32 prev_insn_processed, insn_processed;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b86308896358..d4ea7fd8a967 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19419,7 +19419,7 @@ static int adjust_jmp_off(struct bpf_prog *prog, u32 tgt_idx, u32 delta)
 static int adjust_subprog_starts_after_remove(struct bpf_verifier_env *env,
 					      u32 off, u32 cnt)
 {
-	int i, j;
+	int i, j, first_hidden = env->subprog_cnt - env->hidden_subprog_cnt;
 
 	/* find first prog starting at or after off (first to remove) */
 	for (i = 0; i < env->subprog_cnt; i++)
@@ -19446,6 +19446,8 @@ static int adjust_subprog_starts_after_remove(struct bpf_verifier_env *env,
 			env->subprog_info + j,
 			sizeof(*env->subprog_info) * move);
 		env->subprog_cnt -= j - i;
+		if (first_hidden <= j - 1)
+			env->hidden_subprog_cnt -= j - first_hidden;
 
 		/* remove func_info */
 		if (aux->func_info) {
@@ -21215,15 +21217,20 @@ static int resolve_kfunc_calls(struct bpf_verifier_env *env)
 /* The function requires that first instruction in 'patch' is insnsi[prog->len - 1] */
 static int add_hidden_subprog(struct bpf_verifier_env *env, struct bpf_insn *patch, int len)
 {
-	struct bpf_subprog_info *info = env->subprog_info;
+	struct bpf_subprog_info *info, *tmp;
 	int cnt = env->subprog_cnt;
 	struct bpf_prog *prog;
 
-	/* We only reserve one slot for hidden subprogs in subprog_info. */
-	if (env->hidden_subprog_cnt) {
-		verbose(env, "verifier internal error: only one hidden subprog supported\n");
-		return -EFAULT;
+	if (cnt == env->subprog_cap) {
+		env->subprog_cap *= 2;
+		tmp = vrealloc(env->subprog_info,
+			       array_size(sizeof(*env->subprog_info), env->subprog_cap + 1),
+			       GFP_KERNEL | __GFP_ZERO);
+		if (!tmp)
+			return -ENOMEM;
+		env->subprog_info = tmp;
 	}
+	info = env->subprog_info;
 	/* We're not patching any existing instruction, just appending the new
 	 * ones for the hidden subprog. Hence all of the adjustment operations
 	 * in bpf_patch_insn_data are no-ops.
@@ -23122,6 +23129,13 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
 	ret = -ENOMEM;
 	if (!env->insn_aux_data)
 		goto err_free_env;
+	env->subprog_cap = BPF_MAX_SUBPROGS;
+	env->subprog_info = vzalloc(array_size(sizeof(*env->subprog_info),
+					       env->subprog_cap + 1 /* max + 1 for the fake subprog */));
+	if (!env->subprog_info) {
+		ret = -ENOMEM;
+		goto err_free_env;
+	}
 	for (i = 0; i < len; i++)
 		env->insn_aux_data[i].orig_idx = i;
 	env->prog = *prog;
@@ -23353,8 +23367,9 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
 err_unlock:
 	if (!is_priv)
 		mutex_unlock(&bpf_verifier_lock);
-	vfree(env->insn_aux_data);
 err_free_env:
+	vfree(env->subprog_info);
+	vfree(env->insn_aux_data);
 	kvfree(env);
 	return ret;
 }
-- 
2.47.0