Merge branch 'bpf-direct-packet-access-improvements'

Daniel Borkmann says:

====================
BPF direct packet access improvements

This set adds write support to the currently available read support
for {cls,act}_bpf programs. First one is a fix for affected commit
sitting in net-next and prerequisite for the second one, last patch
adds a number of test cases against the verifier. For details, please
see individual patches.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/bpf.h

@@ -96,6 +96,7 @@ enum bpf_return_type {
 struct bpf_func_proto {
 	u64 (*func)(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
 	bool gpl_only;
+	bool pkt_access;
 	enum bpf_return_type ret_type;
 	enum bpf_arg_type arg1_type;
 	enum bpf_arg_type arg2_type;
@@ -151,7 +152,8 @@ struct bpf_verifier_ops {
 	 */
 	bool (*is_valid_access)(int off, int size, enum bpf_access_type type,
 				enum bpf_reg_type *reg_type);
-
+	int (*gen_prologue)(struct bpf_insn *insn, bool direct_write,
+			    const struct bpf_prog *prog);
 	u32 (*convert_ctx_access)(enum bpf_access_type type, int dst_reg,
 				  int src_reg, int ctx_off,
 				  struct bpf_insn *insn, struct bpf_prog *prog);

include/linux/skbuff.h

@@ -676,13 +676,23 @@ struct sk_buff {
 	 */
 	kmemcheck_bitfield_begin(flags1);
 	__u16			queue_mapping;
+
+/* if you move cloned around you also must adapt those constants */
+#ifdef __BIG_ENDIAN_BITFIELD
+#define CLONED_MASK	(1 << 7)
+#else
+#define CLONED_MASK	1
+#endif
+#define CLONED_OFFSET()		offsetof(struct sk_buff, __cloned_offset)
+
+	__u8			__cloned_offset[0];
 	__u8			cloned:1,
 				nohdr:1,
 				fclone:2,
 				peeked:1,
 				head_frag:1,
-				xmit_more:1;
-	/* one bit hole */
+				xmit_more:1,
+				__unused:1; /* one bit hole */
 	kmemcheck_bitfield_end(flags1);
 
 	/* fields enclosed in headers_start/headers_end are copied

include/uapi/linux/bpf.h

@@ -398,6 +398,27 @@ enum bpf_func_id {
 	 */
 	BPF_FUNC_skb_change_tail,
 
+	/**
+	 * bpf_skb_pull_data(skb, len)
+	 * The helper will pull in non-linear data in case the
+	 * skb is non-linear and not all of len are part of the
+	 * linear section. Only needed for read/write with direct
+	 * packet access.
+	 * @skb: pointer to skb
+	 * @len: len to make read/writeable
+	 * Return: 0 on success or negative error
+	 */
+	BPF_FUNC_skb_pull_data,
+
+	/**
+	 * bpf_csum_update(skb, csum)
+	 * Adds csum into skb->csum in case of CHECKSUM_COMPLETE.
+	 * @skb: pointer to skb
+	 * @csum: csum to add
+	 * Return: csum on success or negative error
+	 */
+	BPF_FUNC_csum_update,
+
 	__BPF_FUNC_MAX_ID,
 };
 

kernel/bpf/helpers.c

@@ -36,6 +36,7 @@ BPF_CALL_2(bpf_map_lookup_elem, struct bpf_map *, map, void *, key)
 const struct bpf_func_proto bpf_map_lookup_elem_proto = {
 	.func		= bpf_map_lookup_elem,
 	.gpl_only	= false,
+	.pkt_access	= true,
 	.ret_type	= RET_PTR_TO_MAP_VALUE_OR_NULL,
 	.arg1_type	= ARG_CONST_MAP_PTR,
 	.arg2_type	= ARG_PTR_TO_MAP_KEY,
@@ -51,6 +52,7 @@ BPF_CALL_4(bpf_map_update_elem, struct bpf_map *, map, void *, key,
 const struct bpf_func_proto bpf_map_update_elem_proto = {
 	.func		= bpf_map_update_elem,
 	.gpl_only	= false,
+	.pkt_access	= true,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_CONST_MAP_PTR,
 	.arg2_type	= ARG_PTR_TO_MAP_KEY,
@@ -67,6 +69,7 @@ BPF_CALL_2(bpf_map_delete_elem, struct bpf_map *, map, void *, key)
 const struct bpf_func_proto bpf_map_delete_elem_proto = {
 	.func		= bpf_map_delete_elem,
 	.gpl_only	= false,
+	.pkt_access	= true,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_CONST_MAP_PTR,
 	.arg2_type	= ARG_PTR_TO_MAP_KEY,

kernel/bpf/verifier.c

@@ -196,6 +196,7 @@ struct verifier_env {
 	u32 used_map_cnt;		/* number of used maps */
 	u32 id_gen;			/* used to generate unique reg IDs */
 	bool allow_ptr_leaks;
+	bool seen_direct_write;
 };
 
 #define BPF_COMPLEXITY_LIMIT_INSNS	65536
@@ -204,6 +205,7 @@ struct verifier_env {
 struct bpf_call_arg_meta {
 	struct bpf_map *map_ptr;
 	bool raw_mode;
+	bool pkt_access;
 	int regno;
 	int access_size;
 };
@@ -654,10 +656,17 @@ static int check_map_access(struct verifier_env *env, u32 regno, int off,
 
 #define MAX_PACKET_OFF 0xffff
 
-static bool may_write_pkt_data(enum bpf_prog_type type)
+static bool may_access_direct_pkt_data(struct verifier_env *env,
+				       const struct bpf_call_arg_meta *meta)
 {
-	switch (type) {
+	switch (env->prog->type) {
+	case BPF_PROG_TYPE_SCHED_CLS:
+	case BPF_PROG_TYPE_SCHED_ACT:
 	case BPF_PROG_TYPE_XDP:
+		if (meta)
+			return meta->pkt_access;
+
+		env->seen_direct_write = true;
 		return true;
 	default:
 		return false;
@@ -671,7 +680,7 @@ static int check_packet_access(struct verifier_env *env, u32 regno, int off,
 	struct reg_state *reg = &regs[regno];
 
 	off += reg->off;
-	if (off < 0 || off + size > reg->range) {
+	if (off < 0 || size <= 0 || off + size > reg->range) {
 		verbose("invalid access to packet, off=%d size=%d, R%d(id=%d,off=%d,r=%d)\n",
 			off, size, regno, reg->id, reg->off, reg->range);
 		return -EACCES;
@@ -817,7 +826,7 @@ static int check_mem_access(struct verifier_env *env, u32 regno, int off,
 			err = check_stack_read(state, off, size, value_regno);
 		}
 	} else if (state->regs[regno].type == PTR_TO_PACKET) {
-		if (t == BPF_WRITE && !may_write_pkt_data(env->prog->type)) {
+		if (t == BPF_WRITE && !may_access_direct_pkt_data(env, NULL)) {
 			verbose("cannot write into packet\n");
 			return -EACCES;
 		}
@@ -950,8 +959,8 @@ static int check_func_arg(struct verifier_env *env, u32 regno,
 		return 0;
 	}
 
-	if (type == PTR_TO_PACKET && !may_write_pkt_data(env->prog->type)) {
-		verbose("helper access to the packet is not allowed for clsact\n");
+	if (type == PTR_TO_PACKET && !may_access_direct_pkt_data(env, meta)) {
+		verbose("helper access to the packet is not allowed\n");
 		return -EACCES;
 	}
 
@@ -1191,6 +1200,7 @@ static int check_call(struct verifier_env *env, int func_id)
 	changes_data = bpf_helper_changes_skb_data(fn->func);
 
 	memset(&meta, 0, sizeof(meta));
+	meta.pkt_access = fn->pkt_access;
 
 	/* We only support one arg being in raw mode at the moment, which
 	 * is sufficient for the helper functions we have right now.
@@ -2675,18 +2685,35 @@ static void convert_pseudo_ld_imm64(struct verifier_env *env)
  */
 static int convert_ctx_accesses(struct verifier_env *env)
 {
-	struct bpf_insn *insn = env->prog->insnsi;
-	int insn_cnt = env->prog->len;
-	struct bpf_insn insn_buf[16];
+	const struct bpf_verifier_ops *ops = env->prog->aux->ops;
+	struct bpf_insn insn_buf[16], *insn;
 	struct bpf_prog *new_prog;
 	enum bpf_access_type type;
-	int i;
+	int i, insn_cnt, cnt;
 
-	if (!env->prog->aux->ops->convert_ctx_access)
+	if (ops->gen_prologue) {
+		cnt = ops->gen_prologue(insn_buf, env->seen_direct_write,
+					env->prog);
+		if (cnt >= ARRAY_SIZE(insn_buf)) {
+			verbose("bpf verifier is misconfigured\n");
+			return -EINVAL;
+		} else if (cnt) {
+			new_prog = bpf_patch_insn_single(env->prog, 0,
+							 insn_buf, cnt);
+			if (!new_prog)
+				return -ENOMEM;
+			env->prog = new_prog;
+		}
+	}
+
+	if (!ops->convert_ctx_access)
 		return 0;
 
+	insn_cnt = env->prog->len;
+	insn = env->prog->insnsi;
+
 	for (i = 0; i < insn_cnt; i++, insn++) {
-		u32 insn_delta, cnt;
+		u32 insn_delta;
 
 		if (insn->code == (BPF_LDX | BPF_MEM | BPF_W) ||
 		    insn->code == (BPF_LDX | BPF_MEM | BPF_DW))
@@ -2703,8 +2730,7 @@ static int convert_ctx_accesses(struct verifier_env *env)
 			continue;
 		}
 
-		cnt = env->prog->aux->ops->
-			convert_ctx_access(type, insn->dst_reg, insn->src_reg,
+		cnt = ops->convert_ctx_access(type, insn->dst_reg, insn->src_reg,
 					      insn->off, insn_buf, env->prog);
 		if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
 			verbose("bpf verifier is misconfigured\n");

net/core/filter.c

@@ -1362,6 +1362,11 @@ static inline int bpf_try_make_writable(struct sk_buff *skb,
 	return err;
 }
 
+static int bpf_try_make_head_writable(struct sk_buff *skb)
+{
+	return bpf_try_make_writable(skb, skb_headlen(skb));
+}
+
 static inline void bpf_push_mac_rcsum(struct sk_buff *skb)
 {
 	if (skb_at_tc_ingress(skb))
@@ -1441,6 +1446,28 @@ static const struct bpf_func_proto bpf_skb_load_bytes_proto = {
 	.arg4_type	= ARG_CONST_STACK_SIZE,
 };
 
+BPF_CALL_2(bpf_skb_pull_data, struct sk_buff *, skb, u32, len)
+{
+	/* Idea is the following: should the needed direct read/write
+	 * test fail during runtime, we can pull in more data and redo
+	 * again, since implicitly, we invalidate previous checks here.
+	 *
+	 * Or, since we know how much we need to make read/writeable,
+	 * this can be done once at the program beginning for direct
+	 * access case. By this we overcome limitations of only current
+	 * headroom being accessible.
+	 */
+	return bpf_try_make_writable(skb, len ? : skb_headlen(skb));
+}
+
+static const struct bpf_func_proto bpf_skb_pull_data_proto = {
+	.func		= bpf_skb_pull_data,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+};
+
 BPF_CALL_5(bpf_l3_csum_replace, struct sk_buff *, skb, u32, offset,
 	   u64, from, u64, to, u64, flags)
 {
@@ -1567,6 +1594,7 @@ BPF_CALL_5(bpf_csum_diff, __be32 *, from, u32, from_size,
 static const struct bpf_func_proto bpf_csum_diff_proto = {
 	.func		= bpf_csum_diff,
 	.gpl_only	= false,
+	.pkt_access	= true,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_STACK,
 	.arg2_type	= ARG_CONST_STACK_SIZE_OR_ZERO,
@@ -1575,6 +1603,26 @@ static const struct bpf_func_proto bpf_csum_diff_proto = {
 	.arg5_type	= ARG_ANYTHING,
 };
 
+BPF_CALL_2(bpf_csum_update, struct sk_buff *, skb, __wsum, csum)
+{
+	/* The interface is to be used in combination with bpf_csum_diff()
+	 * for direct packet writes. csum rotation for alignment as well
+	 * as emulating csum_sub() can be done from the eBPF program.
+	 */
+	if (skb->ip_summed == CHECKSUM_COMPLETE)
+		return (skb->csum = csum_add(skb->csum, csum));
+
+	return -ENOTSUPP;
+}
+
+static const struct bpf_func_proto bpf_csum_update_proto = {
+	.func		= bpf_csum_update,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+};
+
 static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
 {
 	return dev_forward_skb(dev, skb);
@@ -1602,6 +1650,8 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)
 BPF_CALL_3(bpf_clone_redirect, struct sk_buff *, skb, u32, ifindex, u64, flags)
 {
 	struct net_device *dev;
+	struct sk_buff *clone;
+	int ret;
 
 	if (unlikely(flags & ~(BPF_F_INGRESS)))
 		return -EINVAL;
@@ -1610,14 +1660,25 @@ BPF_CALL_3(bpf_clone_redirect, struct sk_buff *, skb, u32, ifindex, u64, flags)
 	if (unlikely(!dev))
 		return -EINVAL;
 
-	skb = skb_clone(skb, GFP_ATOMIC);
-	if (unlikely(!skb))
+	clone = skb_clone(skb, GFP_ATOMIC);
+	if (unlikely(!clone))
 		return -ENOMEM;
 
-	bpf_push_mac_rcsum(skb);
+	/* For direct write, we need to keep the invariant that the skbs
+	 * we're dealing with need to be uncloned. Should uncloning fail
+	 * here, we need to free the just generated clone to unclone once
+	 * again.
+	 */
+	ret = bpf_try_make_head_writable(skb);
+	if (unlikely(ret)) {
+		kfree_skb(clone);
+		return -ENOMEM;
+	}
+
+	bpf_push_mac_rcsum(clone);
 
 	return flags & BPF_F_INGRESS ?
-	       __bpf_rx_skb(dev, skb) : __bpf_tx_skb(dev, skb);
+	       __bpf_rx_skb(dev, clone) : __bpf_tx_skb(dev, clone);
 }
 
 static const struct bpf_func_proto bpf_clone_redirect_proto = {
@@ -2063,19 +2124,14 @@ static const struct bpf_func_proto bpf_skb_change_tail_proto = {
 
 bool bpf_helper_changes_skb_data(void *func)
 {
-	if (func == bpf_skb_vlan_push)
-		return true;
-	if (func == bpf_skb_vlan_pop)
-		return true;
-	if (func == bpf_skb_store_bytes)
-		return true;
-	if (func == bpf_skb_change_proto)
-		return true;
-	if (func == bpf_skb_change_tail)
-		return true;
-	if (func == bpf_l3_csum_replace)
-		return true;
-	if (func == bpf_l4_csum_replace)
+	if (func == bpf_skb_vlan_push ||
+	    func == bpf_skb_vlan_pop ||
+	    func == bpf_skb_store_bytes ||
+	    func == bpf_skb_change_proto ||
+	    func == bpf_skb_change_tail ||
+	    func == bpf_skb_pull_data ||
+	    func == bpf_l3_csum_replace ||
+	    func == bpf_l4_csum_replace)
 		return true;
 
 	return false;
@@ -2440,8 +2496,12 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
 		return &bpf_skb_store_bytes_proto;
 	case BPF_FUNC_skb_load_bytes:
 		return &bpf_skb_load_bytes_proto;
+	case BPF_FUNC_skb_pull_data:
+		return &bpf_skb_pull_data_proto;
 	case BPF_FUNC_csum_diff:
 		return &bpf_csum_diff_proto;
+	case BPF_FUNC_csum_update:
+		return &bpf_csum_update_proto;
 	case BPF_FUNC_l3_csum_replace:
 		return &bpf_l3_csum_replace_proto;
 	case BPF_FUNC_l4_csum_replace:
@@ -2533,6 +2593,45 @@ static bool sk_filter_is_valid_access(int off, int size,
 	return __is_valid_access(off, size, type);
 }
 
+static int tc_cls_act_prologue(struct bpf_insn *insn_buf, bool direct_write,
+			       const struct bpf_prog *prog)
+{
+	struct bpf_insn *insn = insn_buf;
+
+	if (!direct_write)
+		return 0;
+
+	/* if (!skb->cloned)
+	 *       goto start;
+	 *
+	 * (Fast-path, otherwise approximation that we might be
+	 *  a clone, do the rest in helper.)
+	 */
+	*insn++ = BPF_LDX_MEM(BPF_B, BPF_REG_6, BPF_REG_1, CLONED_OFFSET());
+	*insn++ = BPF_ALU32_IMM(BPF_AND, BPF_REG_6, CLONED_MASK);
+	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 7);
+
+	/* ret = bpf_skb_pull_data(skb, 0); */
+	*insn++ = BPF_MOV64_REG(BPF_REG_6, BPF_REG_1);
+	*insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_2, BPF_REG_2);
+	*insn++ = BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
+			       BPF_FUNC_skb_pull_data);
+	/* if (!ret)
+	 *      goto restore;
+	 * return TC_ACT_SHOT;
+	 */
+	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2);
+	*insn++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_0, TC_ACT_SHOT);
+	*insn++ = BPF_EXIT_INSN();
+
+	/* restore: */
+	*insn++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_6);
+	/* start: */
+	*insn++ = prog->insnsi[0];
+
+	return insn - insn_buf;
+}
+
 static bool tc_cls_act_is_valid_access(int off, int size,
 				       enum bpf_access_type type,
 				       enum bpf_reg_type *reg_type)
@@ -2810,6 +2909,7 @@ static const struct bpf_verifier_ops tc_cls_act_ops = {
 	.get_func_proto		= tc_cls_act_func_proto,
 	.is_valid_access	= tc_cls_act_is_valid_access,
 	.convert_ctx_access	= tc_cls_act_convert_ctx_access,
+	.gen_prologue		= tc_cls_act_prologue,
 };
 
 static const struct bpf_verifier_ops xdp_ops = {