Merge branch 'bpf-verifier-resilience'

Alexei Starovoitov says:

====================
Three patches to improve verifier ability to handle pathological bpf
programs with a lot of branches:

- make sure prog_load syscall can be aborted
- improve branch taken analysis
- introduce per-insn complexity limit for unprivileged programs
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/verifier.c

@@ -175,6 +175,7 @@ struct bpf_verifier_stack_elem {
 
 #define BPF_COMPLEXITY_LIMIT_INSNS	131072
 #define BPF_COMPLEXITY_LIMIT_STACK	1024
+#define BPF_COMPLEXITY_LIMIT_STATES	64
 
 #define BPF_MAP_PTR_UNPRIV	1UL
 #define BPF_MAP_PTR_POISON	((void *)((0xeB9FUL << 1) +	\
@@ -3751,6 +3752,79 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate,
 	}
 }
 
+/* compute branch direction of the expression "if (reg opcode val) goto target;"
+ * and return:
+ *  1 - branch will be taken and "goto target" will be executed
+ *  0 - branch will not be taken and fall-through to next insn
+ * -1 - unknown. Example: "if (reg < 5)" is unknown when register value range [0,10]
+ */
+static int is_branch_taken(struct bpf_reg_state *reg, u64 val, u8 opcode)
+{
+	if (__is_pointer_value(false, reg))
+		return -1;
+
+	switch (opcode) {
+	case BPF_JEQ:
+		if (tnum_is_const(reg->var_off))
+			return !!tnum_equals_const(reg->var_off, val);
+		break;
+	case BPF_JNE:
+		if (tnum_is_const(reg->var_off))
+			return !tnum_equals_const(reg->var_off, val);
+		break;
+	case BPF_JGT:
+		if (reg->umin_value > val)
+			return 1;
+		else if (reg->umax_value <= val)
+			return 0;
+		break;
+	case BPF_JSGT:
+		if (reg->smin_value > (s64)val)
+			return 1;
+		else if (reg->smax_value < (s64)val)
+			return 0;
+		break;
+	case BPF_JLT:
+		if (reg->umax_value < val)
+			return 1;
+		else if (reg->umin_value >= val)
+			return 0;
+		break;
+	case BPF_JSLT:
+		if (reg->smax_value < (s64)val)
+			return 1;
+		else if (reg->smin_value >= (s64)val)
+			return 0;
+		break;
+	case BPF_JGE:
+		if (reg->umin_value >= val)
+			return 1;
+		else if (reg->umax_value < val)
+			return 0;
+		break;
+	case BPF_JSGE:
+		if (reg->smin_value >= (s64)val)
+			return 1;
+		else if (reg->smax_value < (s64)val)
+			return 0;
+		break;
+	case BPF_JLE:
+		if (reg->umax_value <= val)
+			return 1;
+		else if (reg->umin_value > val)
+			return 0;
+		break;
+	case BPF_JSLE:
+		if (reg->smax_value <= (s64)val)
+			return 1;
+		else if (reg->smin_value > (s64)val)
+			return 0;
+		break;
+	}
+
+	return -1;
+}
+
 /* Adjusts the register min/max values in the case that the dst_reg is the
  * variable register that we are working on, and src_reg is a constant or we're
  * simply doing a BPF_K check.
@@ -4152,21 +4226,15 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
 
 	dst_reg = &regs[insn->dst_reg];
 
-	/* detect if R == 0 where R was initialized to zero earlier */
-	if (BPF_SRC(insn->code) == BPF_K &&
-	    (opcode == BPF_JEQ || opcode == BPF_JNE) &&
-	    dst_reg->type == SCALAR_VALUE &&
-	    tnum_is_const(dst_reg->var_off)) {
-		if ((opcode == BPF_JEQ && dst_reg->var_off.value == insn->imm) ||
-		    (opcode == BPF_JNE && dst_reg->var_off.value != insn->imm)) {
-			/* if (imm == imm) goto pc+off;
-			 * only follow the goto, ignore fall-through
-			 */
+	if (BPF_SRC(insn->code) == BPF_K) {
+		int pred = is_branch_taken(dst_reg, insn->imm, opcode);
+
+		if (pred == 1) {
+			 /* only follow the goto, ignore fall-through */
 			*insn_idx += insn->off;
 			return 0;
-		} else {
-			/* if (imm != imm) goto pc+off;
-			 * only follow fall-through branch, since
+		} else if (pred == 0) {
+			/* only follow fall-through branch, since
 			 * that's where the program will go
 			 */
 			return 0;
@@ -4980,7 +5048,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 	struct bpf_verifier_state_list *new_sl;
 	struct bpf_verifier_state_list *sl;
 	struct bpf_verifier_state *cur = env->cur_state, *new;
-	int i, j, err;
+	int i, j, err, states_cnt = 0;
 
 	sl = env->explored_states[insn_idx];
 	if (!sl)
@@ -5007,8 +5075,12 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 			return 1;
 		}
 		sl = sl->next;
+		states_cnt++;
 	}
 
+	if (!env->allow_ptr_leaks && states_cnt > BPF_COMPLEXITY_LIMIT_STATES)
+		return 0;
+
 	/* there were no equivalent states, remember current one.
 	 * technically the current state is not proven to be safe yet,
 	 * but it will either reach outer most bpf_exit (which means it's safe)
@@ -5148,6 +5220,9 @@ static int do_check(struct bpf_verifier_env *env)
 			goto process_bpf_exit;
 		}
 
+		if (signal_pending(current))
+			return -EAGAIN;
+
 		if (need_resched())
 			cond_resched();
 

tools/testing/selftests/bpf/test_verifier.c

@@ -8576,7 +8576,7 @@ static struct bpf_test tests[] = {
 			BPF_JMP_IMM(BPF_JA, 0, 0, -7),
 		},
 		.fixup_map_hash_8b = { 4 },
-		.errstr = "R0 invalid mem access 'inv'",
+		.errstr = "unbounded min value",
 		.result = REJECT,
 	},
 	{
@@ -10547,7 +10547,7 @@ static struct bpf_test tests[] = {
 		"check deducing bounds from const, 5",
 		.insns = {
 			BPF_MOV64_IMM(BPF_REG_0, 0),
-			BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 0, 1),
+			BPF_JMP_IMM(BPF_JSGE, BPF_REG_0, 1, 1),
 			BPF_ALU64_REG(BPF_SUB, BPF_REG_0, BPF_REG_1),
 			BPF_EXIT_INSN(),
 		},