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Date: Mon, 7 May 2018 06:22:43 -0400
From: Jiong Wang <jiong.wang@...ronome.com>
To: alexei.starovoitov@...il.com, daniel@...earbox.net
Cc: john.fastabend@...il.com, netdev@...r.kernel.org,
oss-drivers@...ronome.com, Jiong Wang <jiong.wang@...ronome.com>
Subject: [RFC bpf-next 07/10] bpf: cfg: build call graph and detect unreachable/recursive call
This patch build call graph during insn scan inside check_subprogs.
Then do recursive and unreachable subprog detection using call graph.
Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
---
include/linux/bpf_verifier.h | 1 +
kernel/bpf/cfg.c | 133 +++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/cfg.h | 4 ++
kernel/bpf/verifier.c | 32 +++++++++--
4 files changed, 166 insertions(+), 4 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 9c0a808..96337ba 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -176,6 +176,7 @@ static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log)
struct bpf_subprog_info {
u32 start; /* insn idx of function entry point */
u16 stack_depth; /* max. stack depth used by this function */
+ struct list_head callees; /* callees list. */
struct list_head bbs; /* basic blocks list. */
u32 bb_num; /* total basic block num. */
unsigned long *dtree;
diff --git a/kernel/bpf/cfg.c b/kernel/bpf/cfg.c
index a34a95c..174e3f0 100644
--- a/kernel/bpf/cfg.c
+++ b/kernel/bpf/cfg.c
@@ -13,6 +13,12 @@
#include "cfg.h"
+struct cedge_node {
+ struct list_head l;
+ u8 caller_idx;
+ u8 callee_idx;
+};
+
struct edge_node {
struct list_head l;
struct bb_node *src;
@@ -652,6 +658,126 @@ int add_subprog(struct bpf_verifier_env *env, int off)
return 0;
}
+struct callee_iter {
+ struct list_head *list_head;
+ struct cedge_node *callee;
+};
+
+#define first_callee(c_list) list_first_entry(c_list, struct cedge_node, l)
+#define next_callee(c) list_next_entry(c, l)
+
+static bool ci_end_p(struct callee_iter *ci)
+{
+ return &ci->callee->l == ci->list_head;
+}
+
+static void ci_next(struct callee_iter *ci)
+{
+ struct cedge_node *c = ci->callee;
+
+ ci->callee = next_callee(c);
+}
+
+#define EXPLORING 1
+#define EXPLORED 2
+int cgraph_check_recursive_unreachable(struct bpf_verifier_env *env,
+ struct bpf_subprog_info *subprog)
+{
+ struct callee_iter *stack;
+ struct cedge_node *callee;
+ int sp = 0, idx = 0, ret;
+ struct callee_iter ci;
+ int *status;
+
+ stack = kmalloc_array(128, sizeof(struct callee_iter), GFP_KERNEL);
+ if (!stack)
+ return -ENOMEM;
+ status = kcalloc(env->subprog_cnt, sizeof(int), GFP_KERNEL);
+ if (!status) {
+ kfree(stack);
+ return -ENOMEM;
+ }
+ ci.callee = first_callee(&subprog->callees);
+ ci.list_head = &subprog->callees;
+ status[0] = EXPLORING;
+
+ while (1) {
+ while (!ci_end_p(&ci)) {
+ callee = ci.callee;
+ idx = callee->callee_idx;
+ if (status[idx] == EXPLORING) {
+ bpf_verifier_log_write(env, "cgraph - recursive call\n");
+ ret = -EINVAL;
+ goto err_free;
+ }
+
+ status[idx] = EXPLORING;
+
+ if (sp == 127) {
+ bpf_verifier_log_write(env, "cgraph - call frame too deep\n");
+ ret = -EINVAL;
+ goto err_free;
+ }
+
+ stack[sp++] = ci;
+ ci.callee = first_callee(&subprog[idx].callees);
+ ci.list_head = &subprog[idx].callees;
+ }
+
+ if (!list_empty(ci.list_head))
+ status[first_callee(ci.list_head)->caller_idx] =
+ EXPLORED;
+ else
+ /* leaf func. */
+ status[idx] = EXPLORED;
+
+ if (!sp)
+ break;
+
+ ci = stack[--sp];
+ ci_next(&ci);
+ }
+
+ for (idx = 0; idx < env->subprog_cnt; idx++)
+ if (status[idx] != EXPLORED) {
+ bpf_verifier_log_write(env, "cgraph - unreachable subprog\n");
+ ret = -EINVAL;
+ goto err_free;
+ }
+
+ ret = 0;
+err_free:
+ kfree(status);
+ kfree(stack);
+ return ret;
+}
+
+int subprog_append_callee(struct bpf_verifier_env *env,
+ struct list_head *callees_list,
+ int caller_idx, int off)
+{
+ int callee_idx = find_subprog(env, off);
+ struct cedge_node *new_callee, *callee;
+
+ if (callee_idx < 0)
+ return callee_idx;
+
+ list_for_each_entry(callee, callees_list, l) {
+ if (callee->callee_idx == callee_idx)
+ return 0;
+ }
+
+ new_callee = kzalloc(sizeof(*new_callee), GFP_KERNEL);
+ if (!new_callee)
+ return -ENOMEM;
+
+ new_callee->caller_idx = caller_idx;
+ new_callee->callee_idx = callee_idx;
+ list_add_tail(&new_callee->l, callees_list);
+
+ return 0;
+}
+
static void subprog_free_edge(struct bb_node *bb)
{
struct list_head *succs = &bb->e_succs;
@@ -669,7 +795,9 @@ void subprog_free(struct bpf_subprog_info *subprog, int end_idx)
int i = 0;
for (; i <= end_idx; i++) {
+ struct list_head *callees = &subprog[i].callees;
struct list_head *bbs = &subprog[i].bbs;
+ struct cedge_node *callee, *tmp_callee;
struct bb_node *bb, *tmp, *exit;
bb = entry_bb(bbs);
@@ -680,6 +808,11 @@ void subprog_free(struct bpf_subprog_info *subprog, int end_idx)
kfree(bb);
}
+ list_for_each_entry_safe(callee, tmp_callee, callees, l) {
+ list_del(&callee->l);
+ kfree(callee);
+ }
+
if (subprog[i].dtree_avail)
kfree(subprog[i].dtree);
}
diff --git a/kernel/bpf/cfg.h b/kernel/bpf/cfg.h
index 57eab9b..577c22c 100644
--- a/kernel/bpf/cfg.h
+++ b/kernel/bpf/cfg.h
@@ -9,9 +9,13 @@
#define __BPF_CFG_H__
int add_subprog(struct bpf_verifier_env *env, int off);
+int cgraph_check_recursive_unreachable(struct bpf_verifier_env *env,
+ struct bpf_subprog_info *subprog);
int find_subprog(struct bpf_verifier_env *env, int off);
int subprog_add_bb_edges(struct bpf_insn *insns, struct list_head *bb_list);
int subprog_append_bb(struct list_head *bb_list, int head);
+int subprog_append_callee(struct bpf_verifier_env *env,
+ struct list_head *bb_list, int caller_idx, int off);
int subprog_build_dom_info(struct bpf_verifier_env *env,
struct bpf_subprog_info *subprog);
int subprog_fini_bb(struct list_head *bb_list, int subprog_end);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 72bda84..12f5399 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -739,9 +739,9 @@ static int check_subprogs(struct bpf_verifier_env *env)
{
int i, ret, subprog_start, subprog_end, off, cur_subprog = 0;
struct bpf_subprog_info *subprog = env->subprog_info;
+ struct list_head *cur_bb_list, *cur_callee_list;
struct bpf_insn *insn = env->prog->insnsi;
int insn_cnt = env->prog->len;
- struct list_head *cur_bb_list;
/* Add entry function. */
ret = add_subprog(env, 0);
@@ -772,16 +772,23 @@ static int check_subprogs(struct bpf_verifier_env *env)
*/
subprog[env->subprog_cnt].start = insn_cnt;
- if (env->log.level > 1)
- for (i = 0; i < env->subprog_cnt; i++)
+ for (i = 0; i < env->subprog_cnt; i++) {
+ if (env->log.level > 1)
verbose(env, "func#%d @%d\n", i, subprog[i].start);
+ /* Don't init callees inside add_subprog which will sort the
+ * array which breaks list link.
+ */
+ INIT_LIST_HEAD(&subprog[i].callees);
+ }
+
subprog_start = subprog[cur_subprog].start;
subprog_end = subprog[cur_subprog + 1].start;
cur_bb_list = &subprog[cur_subprog].bbs;
ret = subprog_init_bb(cur_bb_list, subprog_start);
if (ret < 0)
goto free_nodes;
+ cur_callee_list = &env->subprog_info[cur_subprog].callees;
/* now check that all jumps are within the same subprog */
for (i = 0; i < insn_cnt; i++) {
u8 code = insn[i].code;
@@ -798,8 +805,20 @@ static int check_subprogs(struct bpf_verifier_env *env)
goto next;
}
- if (BPF_OP(code) == BPF_CALL)
+ if (BPF_OP(code) == BPF_CALL) {
+ if (insn[i].src_reg == BPF_PSEUDO_CALL) {
+ int target = i + insn[i].imm + 1;
+
+ ret = subprog_append_callee(env,
+ cur_callee_list,
+ cur_subprog,
+ target);
+ if (ret < 0)
+ return ret;
+ }
+
goto next;
+ }
off = i + insn[i].off + 1;
if (off < subprog_start || off >= subprog_end) {
@@ -855,10 +874,15 @@ static int check_subprogs(struct bpf_verifier_env *env)
subprog_start);
if (ret < 0)
goto free_nodes;
+ cur_callee_list = &subprog[cur_subprog].callees;
}
}
}
+ ret = cgraph_check_recursive_unreachable(env, env->subprog_info);
+ if (ret < 0)
+ goto free_nodes;
+
ret = 0;
free_nodes:
--
2.7.4
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