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Message-ID: <20180601093258.15353.34877.stgit@john-Precision-Tower-5810>
Date: Fri, 01 Jun 2018 02:32:58 -0700
From: John Fastabend <john.fastabend@...il.com>
To: alexei.starovoitov@...il.com, daniel@...earbox.net,
davem@...emloft.net
Cc: netdev@...r.kernel.org
Subject: [RFC PATCH 08/16] bpf: cfg: remove push_insn and check_cfg
From: Jiong Wang <jiong.wang@...ronome.com>
As we have detected loop and unreachable insns based on domination
information and call graph, there is no need of check_cfg.
This patch removes check_cfg and it's associated push_insn.
state prune heuristic marking as moved to check_subprog.
Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
---
kernel/bpf/verifier.c | 228 +++----------------------------------------------
1 file changed, 16 insertions(+), 212 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ddba8ad..338ebc5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -760,6 +760,8 @@ enum reg_arg_type {
DST_OP_NO_MARK /* same as above, check only, don't mark */
};
+#define STATE_LIST_MARK ((struct bpf_verifier_state_list *)-1L)
+
static int check_subprogs(struct bpf_verifier_env *env)
{
int i, ret, subprog_start, subprog_end, off, cur_subprog = 0;
@@ -840,8 +842,14 @@ static int check_subprogs(struct bpf_verifier_env *env)
target);
if (ret < 0)
return ret;
+
+ env->explored_states[target] = STATE_LIST_MARK;
+ env->explored_states[i] = STATE_LIST_MARK;
}
+ if (i + 1 < insn_cnt)
+ env->explored_states[i + 1] = STATE_LIST_MARK;
+
goto next;
}
@@ -861,6 +869,13 @@ static int check_subprogs(struct bpf_verifier_env *env)
if (ret < 0)
goto free_nodes;
}
+
+ if (BPF_OP(code) != BPF_JA) {
+ env->explored_states[i] = STATE_LIST_MARK;
+ env->explored_states[off] = STATE_LIST_MARK;
+ } else if (i + 1 < insn_cnt) {
+ env->explored_states[i + 1] = STATE_LIST_MARK;
+ }
next:
if (i == subprog_end - 1) {
/* to avoid fall-through from one subprog into another
@@ -4093,217 +4108,6 @@ static int check_return_code(struct bpf_verifier_env *env)
return 0;
}
-/* non-recursive DFS pseudo code
- * 1 procedure DFS-iterative(G,v):
- * 2 label v as discovered
- * 3 let S be a stack
- * 4 S.push(v)
- * 5 while S is not empty
- * 6 t <- S.pop()
- * 7 if t is what we're looking for:
- * 8 return t
- * 9 for all edges e in G.adjacentEdges(t) do
- * 10 if edge e is already labelled
- * 11 continue with the next edge
- * 12 w <- G.adjacentVertex(t,e)
- * 13 if vertex w is not discovered and not explored
- * 14 label e as tree-edge
- * 15 label w as discovered
- * 16 S.push(w)
- * 17 continue at 5
- * 18 else if vertex w is discovered
- * 19 label e as back-edge
- * 20 else
- * 21 // vertex w is explored
- * 22 label e as forward- or cross-edge
- * 23 label t as explored
- * 24 S.pop()
- *
- * convention:
- * 0x10 - discovered
- * 0x11 - discovered and fall-through edge labelled
- * 0x12 - discovered and fall-through and branch edges labelled
- * 0x20 - explored
- */
-
-enum {
- DISCOVERED = 0x10,
- EXPLORED = 0x20,
- FALLTHROUGH = 1,
- BRANCH = 2,
-};
-
-#define STATE_LIST_MARK ((struct bpf_verifier_state_list *) -1L)
-
-static int *insn_stack; /* stack of insns to process */
-static int cur_stack; /* current stack index */
-static int *insn_state;
-
-/* t, w, e - match pseudo-code above:
- * t - index of current instruction
- * w - next instruction
- * e - edge
- */
-static int push_insn(int t, int w, int e, struct bpf_verifier_env *env)
-{
- if (e == FALLTHROUGH && insn_state[t] >= (DISCOVERED | FALLTHROUGH))
- return 0;
-
- if (e == BRANCH && insn_state[t] >= (DISCOVERED | BRANCH))
- return 0;
-
- if (w < 0 || w >= env->prog->len) {
- verbose(env, "jump out of range from insn %d to %d\n", t, w);
- return -EINVAL;
- }
-
- if (e == BRANCH)
- /* mark branch target for state pruning */
- env->explored_states[w] = STATE_LIST_MARK;
-
- if (insn_state[w] == 0) {
- /* tree-edge */
- insn_state[t] = DISCOVERED | e;
- insn_state[w] = DISCOVERED;
- if (cur_stack >= env->prog->len)
- return -E2BIG;
- insn_stack[cur_stack++] = w;
- return 1;
- } else if ((insn_state[w] & 0xF0) == DISCOVERED) {
- verbose(env, "back-edge from insn %d to %d\n", t, w);
- return -EINVAL;
- } else if (insn_state[w] == EXPLORED) {
- /* forward- or cross-edge */
- insn_state[t] = DISCOVERED | e;
- } else {
- verbose(env, "insn state internal bug\n");
- return -EFAULT;
- }
- return 0;
-}
-
-/* non-recursive depth-first-search to detect loops in BPF program
- * loop == back-edge in directed graph
- */
-static int check_cfg(struct bpf_verifier_env *env)
-{
- struct bpf_insn *insns = env->prog->insnsi;
- int insn_cnt = env->prog->len;
- int ret = 0;
- int i, t;
-
- ret = check_subprogs(env);
- if (ret < 0)
- return ret;
-
- insn_state = kcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
- if (!insn_state)
- return -ENOMEM;
-
- insn_stack = kcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
- if (!insn_stack) {
- kfree(insn_state);
- return -ENOMEM;
- }
-
- insn_state[0] = DISCOVERED; /* mark 1st insn as discovered */
- insn_stack[0] = 0; /* 0 is the first instruction */
- cur_stack = 1;
-
-peek_stack:
- if (cur_stack == 0)
- goto check_state;
- t = insn_stack[cur_stack - 1];
-
- if (BPF_CLASS(insns[t].code) == BPF_JMP) {
- u8 opcode = BPF_OP(insns[t].code);
-
- if (opcode == BPF_EXIT) {
- goto mark_explored;
- } else if (opcode == BPF_CALL) {
- ret = push_insn(t, t + 1, FALLTHROUGH, env);
- if (ret == 1)
- goto peek_stack;
- else if (ret < 0)
- goto err_free;
- if (t + 1 < insn_cnt)
- env->explored_states[t + 1] = STATE_LIST_MARK;
- if (insns[t].src_reg == BPF_PSEUDO_CALL) {
- env->explored_states[t] = STATE_LIST_MARK;
- ret = push_insn(t, t + insns[t].imm + 1, BRANCH, env);
- if (ret == 1)
- goto peek_stack;
- else if (ret < 0)
- goto err_free;
- }
- } else if (opcode == BPF_JA) {
- if (BPF_SRC(insns[t].code) != BPF_K) {
- ret = -EINVAL;
- goto err_free;
- }
- /* unconditional jump with single edge */
- ret = push_insn(t, t + insns[t].off + 1,
- FALLTHROUGH, env);
- if (ret == 1)
- goto peek_stack;
- else if (ret < 0)
- goto err_free;
- /* tell verifier to check for equivalent states
- * after every call and jump
- */
- if (t + 1 < insn_cnt)
- env->explored_states[t + 1] = STATE_LIST_MARK;
- } else {
- /* conditional jump with two edges */
- env->explored_states[t] = STATE_LIST_MARK;
- ret = push_insn(t, t + 1, FALLTHROUGH, env);
- if (ret == 1)
- goto peek_stack;
- else if (ret < 0)
- goto err_free;
-
- ret = push_insn(t, t + insns[t].off + 1, BRANCH, env);
- if (ret == 1)
- goto peek_stack;
- else if (ret < 0)
- goto err_free;
- }
- } else {
- /* all other non-branch instructions with single
- * fall-through edge
- */
- ret = push_insn(t, t + 1, FALLTHROUGH, env);
- if (ret == 1)
- goto peek_stack;
- else if (ret < 0)
- goto err_free;
- }
-
-mark_explored:
- insn_state[t] = EXPLORED;
- if (cur_stack-- <= 0) {
- verbose(env, "pop stack internal bug\n");
- ret = -EFAULT;
- goto err_free;
- }
- goto peek_stack;
-
-check_state:
- for (i = 0; i < insn_cnt; i++) {
- if (insn_state[i] != EXPLORED) {
- verbose(env, "unreachable insn %d\n", i);
- ret = -EINVAL;
- goto err_free;
- }
- }
- ret = 0; /* cfg looks good */
-
-err_free:
- kfree(insn_state);
- kfree(insn_stack);
- return ret;
-}
-
/* check %cur's range satisfies %old's */
static bool range_within(struct bpf_reg_state *old,
struct bpf_reg_state *cur)
@@ -5914,7 +5718,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
env->allow_ptr_leaks = capable(CAP_SYS_ADMIN);
- ret = check_cfg(env);
+ ret = check_subprogs(env);
if (ret < 0)
goto skip_full_check;
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