Commit 0a58a65c authored by Daniel Borkmann's avatar Daniel Borkmann
Browse files

Merge branch 'bpf-ptrs-beyond-pkt-end' 



Alexei Starovoitov says:

====================
v1->v2:
- removed set-but-unused variable.
- added Jiri's Tested-by.

In some cases LLVM uses the knowledge that branch is taken to optimze the code
which causes the verifier to reject valid programs.
Teach the verifier to recognize that
r1 = skb->data;
r1 += 10;
r2 = skb->data_end;
if (r1 > r2) {
  here r1 points beyond packet_end and subsequent
  if (r1 > r2) // always evaluates to "true".
}
====================

Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parents c3653879 cb62d340

include/linux/bpf_verifier.h

+1 −1
Original line number Diff line number Diff line
@@ -45,7 +45,7 @@ struct bpf_reg_state { 
	enum bpf_reg_type type;

	union {

		/* valid when type == PTR_TO_PACKET */

		u16 range;

		int range;



		/* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |

		 *   PTR_TO_MAP_VALUE_OR_NULL

kernel/bpf/verifier.c

+107 −22
Original line number Diff line number Diff line
@@ -2739,7 +2739,9 @@ static int check_packet_access(struct bpf_verifier_env *env, u32 regno, int off, 
			regno);

		return -EACCES;

	}

	err = __check_mem_access(env, regno, off, size, reg->range,



	err = reg->range < 0 ? -EINVAL :

	      __check_mem_access(env, regno, off, size, reg->range,

				 zero_size_allowed);

	if (err) {

		verbose(env, "R%d offset is outside of the packet\n", regno);
@@ -4697,6 +4699,32 @@ static void clear_all_pkt_pointers(struct bpf_verifier_env *env) 
		__clear_all_pkt_pointers(env, vstate->frame[i]);

}



enum {

	AT_PKT_END = -1,

	BEYOND_PKT_END = -2,

};



static void mark_pkt_end(struct bpf_verifier_state *vstate, int regn, bool range_open)

{

	struct bpf_func_state *state = vstate->frame[vstate->curframe];

	struct bpf_reg_state *reg = &state->regs[regn];



	if (reg->type != PTR_TO_PACKET)

		/* PTR_TO_PACKET_META is not supported yet */

		return;



	/* The 'reg' is pkt > pkt_end or pkt >= pkt_end.

	 * How far beyond pkt_end it goes is unknown.

	 * if (!range_open) it's the case of pkt >= pkt_end

	 * if (range_open) it's the case of pkt > pkt_end

	 * hence this pointer is at least 1 byte bigger than pkt_end

	 */

	if (range_open)

		reg->range = BEYOND_PKT_END;

	else

		reg->range = AT_PKT_END;

}



static void release_reg_references(struct bpf_verifier_env *env,

				   struct bpf_func_state *state,

				   int ref_obj_id)
@@ -6708,7 +6736,7 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn) 


static void __find_good_pkt_pointers(struct bpf_func_state *state,

				     struct bpf_reg_state *dst_reg,

				     enum bpf_reg_type type, u16 new_range)

				     enum bpf_reg_type type, int new_range)

{

	struct bpf_reg_state *reg;

	int i;
@@ -6733,8 +6761,7 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate, 
				   enum bpf_reg_type type,

				   bool range_right_open)

{

	u16 new_range;

	int i;

	int new_range, i;



	if (dst_reg->off < 0 ||

	    (dst_reg->off == 0 && range_right_open))
@@ -6985,6 +7012,67 @@ static int is_branch_taken(struct bpf_reg_state *reg, u64 val, u8 opcode, 
	return is_branch64_taken(reg, val, opcode);

}



static int flip_opcode(u32 opcode)

{

	/* How can we transform "a <op> b" into "b <op> a"? */

	static const u8 opcode_flip[16] = {

		/* these stay the same */

		[BPF_JEQ  >> 4] = BPF_JEQ,

		[BPF_JNE  >> 4] = BPF_JNE,

		[BPF_JSET >> 4] = BPF_JSET,

		/* these swap "lesser" and "greater" (L and G in the opcodes) */

		[BPF_JGE  >> 4] = BPF_JLE,

		[BPF_JGT  >> 4] = BPF_JLT,

		[BPF_JLE  >> 4] = BPF_JGE,

		[BPF_JLT  >> 4] = BPF_JGT,

		[BPF_JSGE >> 4] = BPF_JSLE,

		[BPF_JSGT >> 4] = BPF_JSLT,

		[BPF_JSLE >> 4] = BPF_JSGE,

		[BPF_JSLT >> 4] = BPF_JSGT

	};

	return opcode_flip[opcode >> 4];

}



static int is_pkt_ptr_branch_taken(struct bpf_reg_state *dst_reg,

				   struct bpf_reg_state *src_reg,

				   u8 opcode)

{

	struct bpf_reg_state *pkt;



	if (src_reg->type == PTR_TO_PACKET_END) {

		pkt = dst_reg;

	} else if (dst_reg->type == PTR_TO_PACKET_END) {

		pkt = src_reg;

		opcode = flip_opcode(opcode);

	} else {

		return -1;

	}



	if (pkt->range >= 0)

		return -1;



	switch (opcode) {

	case BPF_JLE:

		/* pkt <= pkt_end */

		fallthrough;

	case BPF_JGT:

		/* pkt > pkt_end */

		if (pkt->range == BEYOND_PKT_END)

			/* pkt has at last one extra byte beyond pkt_end */

			return opcode == BPF_JGT;

		break;

	case BPF_JLT:

		/* pkt < pkt_end */

		fallthrough;

	case BPF_JGE:

		/* pkt >= pkt_end */

		if (pkt->range == BEYOND_PKT_END || pkt->range == AT_PKT_END)

			return opcode == BPF_JGE;

		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.
@@ -7148,23 +7236,7 @@ static void reg_set_min_max_inv(struct bpf_reg_state *true_reg, 
				u64 val, u32 val32,

				u8 opcode, bool is_jmp32)

{

	/* How can we transform "a <op> b" into "b <op> a"? */

	static const u8 opcode_flip[16] = {

		/* these stay the same */

		[BPF_JEQ  >> 4] = BPF_JEQ,

		[BPF_JNE  >> 4] = BPF_JNE,

		[BPF_JSET >> 4] = BPF_JSET,

		/* these swap "lesser" and "greater" (L and G in the opcodes) */

		[BPF_JGE  >> 4] = BPF_JLE,

		[BPF_JGT  >> 4] = BPF_JLT,

		[BPF_JLE  >> 4] = BPF_JGE,

		[BPF_JLT  >> 4] = BPF_JGT,

		[BPF_JSGE >> 4] = BPF_JSLE,

		[BPF_JSGT >> 4] = BPF_JSLT,

		[BPF_JSLE >> 4] = BPF_JSGE,

		[BPF_JSLT >> 4] = BPF_JSGT

	};

	opcode = opcode_flip[opcode >> 4];

	opcode = flip_opcode(opcode);

	/* This uses zero as "not present in table"; luckily the zero opcode,

	 * BPF_JA, can't get here.

	 */
@@ -7346,6 +7418,7 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn, 
			/* pkt_data' > pkt_end, pkt_meta' > pkt_data */

			find_good_pkt_pointers(this_branch, dst_reg,

					       dst_reg->type, false);

			mark_pkt_end(other_branch, insn->dst_reg, true);

		} else if ((dst_reg->type == PTR_TO_PACKET_END &&

			    src_reg->type == PTR_TO_PACKET) ||

			   (reg_is_init_pkt_pointer(dst_reg, PTR_TO_PACKET) &&
@@ -7353,6 +7426,7 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn, 
			/* pkt_end > pkt_data', pkt_data > pkt_meta' */

			find_good_pkt_pointers(other_branch, src_reg,

					       src_reg->type, true);

			mark_pkt_end(this_branch, insn->src_reg, false);

		} else {

			return false;

		}
@@ -7365,6 +7439,7 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn, 
			/* pkt_data' < pkt_end, pkt_meta' < pkt_data */

			find_good_pkt_pointers(other_branch, dst_reg,

					       dst_reg->type, true);

			mark_pkt_end(this_branch, insn->dst_reg, false);

		} else if ((dst_reg->type == PTR_TO_PACKET_END &&

			    src_reg->type == PTR_TO_PACKET) ||

			   (reg_is_init_pkt_pointer(dst_reg, PTR_TO_PACKET) &&
@@ -7372,6 +7447,7 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn, 
			/* pkt_end < pkt_data', pkt_data > pkt_meta' */

			find_good_pkt_pointers(this_branch, src_reg,

					       src_reg->type, false);

			mark_pkt_end(other_branch, insn->src_reg, true);

		} else {

			return false;

		}
@@ -7384,6 +7460,7 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn, 
			/* pkt_data' >= pkt_end, pkt_meta' >= pkt_data */

			find_good_pkt_pointers(this_branch, dst_reg,

					       dst_reg->type, true);

			mark_pkt_end(other_branch, insn->dst_reg, false);

		} else if ((dst_reg->type == PTR_TO_PACKET_END &&

			    src_reg->type == PTR_TO_PACKET) ||

			   (reg_is_init_pkt_pointer(dst_reg, PTR_TO_PACKET) &&
@@ -7391,6 +7468,7 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn, 
			/* pkt_end >= pkt_data', pkt_data >= pkt_meta' */

			find_good_pkt_pointers(other_branch, src_reg,

					       src_reg->type, false);

			mark_pkt_end(this_branch, insn->src_reg, true);

		} else {

			return false;

		}
@@ -7403,6 +7481,7 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn, 
			/* pkt_data' <= pkt_end, pkt_meta' <= pkt_data */

			find_good_pkt_pointers(other_branch, dst_reg,

					       dst_reg->type, false);

			mark_pkt_end(this_branch, insn->dst_reg, true);

		} else if ((dst_reg->type == PTR_TO_PACKET_END &&

			    src_reg->type == PTR_TO_PACKET) ||

			   (reg_is_init_pkt_pointer(dst_reg, PTR_TO_PACKET) &&
@@ -7410,6 +7489,7 @@ static bool try_match_pkt_pointers(const struct bpf_insn *insn, 
			/* pkt_end <= pkt_data', pkt_data <= pkt_meta' */

			find_good_pkt_pointers(this_branch, src_reg,

					       src_reg->type, true);

			mark_pkt_end(other_branch, insn->src_reg, false);

		} else {

			return false;

		}
@@ -7509,6 +7589,10 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, 
				       src_reg->var_off.value,

				       opcode,

				       is_jmp32);

	} else if (reg_is_pkt_pointer_any(dst_reg) &&

		   reg_is_pkt_pointer_any(src_reg) &&

		   !is_jmp32) {

		pred = is_pkt_ptr_branch_taken(dst_reg, src_reg, opcode);

	}



	if (pred >= 0) {
@@ -7517,7 +7601,8 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, 
		 */

		if (!__is_pointer_value(false, dst_reg))

			err = mark_chain_precision(env, insn->dst_reg);

		if (BPF_SRC(insn->code) == BPF_X && !err)

		if (BPF_SRC(insn->code) == BPF_X && !err &&

		    !__is_pointer_value(false, src_reg))

			err = mark_chain_precision(env, insn->src_reg);

		if (err)

			return err;

tools/testing/selftests/bpf/prog_tests/test_skb_pkt_end.c

0 → 100644
+41 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/* Copyright (c) 2020 Facebook */

#include <test_progs.h>

#include <network_helpers.h>

#include "skb_pkt_end.skel.h"



static int sanity_run(struct bpf_program *prog)

{

	__u32 duration, retval;

	int err, prog_fd;



	prog_fd = bpf_program__fd(prog);

	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),

				NULL, NULL, &retval, &duration);

	if (CHECK(err || retval != 123, "test_run",

		  "err %d errno %d retval %d duration %d\n",

		  err, errno, retval, duration))

		return -1;

	return 0;

}



void test_test_skb_pkt_end(void)

{

	struct skb_pkt_end *skb_pkt_end_skel = NULL;

	__u32 duration = 0;

	int err;



	skb_pkt_end_skel = skb_pkt_end__open_and_load();

	if (CHECK(!skb_pkt_end_skel, "skb_pkt_end_skel_load", "skb_pkt_end skeleton failed\n"))

		goto cleanup;



	err = skb_pkt_end__attach(skb_pkt_end_skel);

	if (CHECK(err, "skb_pkt_end_attach", "skb_pkt_end attach failed: %d\n", err))

		goto cleanup;



	if (sanity_run(skb_pkt_end_skel->progs.main_prog))

		goto cleanup;



cleanup:

	skb_pkt_end__destroy(skb_pkt_end_skel);

}

tools/testing/selftests/bpf/progs/skb_pkt_end.c

0 → 100644
+54 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#define BPF_NO_PRESERVE_ACCESS_INDEX

#include <vmlinux.h>

#include <bpf/bpf_core_read.h>

#include <bpf/bpf_helpers.h>



#define NULL 0

#define INLINE __always_inline



#define skb_shorter(skb, len) ((void *)(long)(skb)->data + (len) > (void *)(long)skb->data_end)



#define ETH_IPV4_TCP_SIZE (14 + sizeof(struct iphdr) + sizeof(struct tcphdr))



static INLINE struct iphdr *get_iphdr(struct __sk_buff *skb)

{

	struct iphdr *ip = NULL;

	struct ethhdr *eth;



	if (skb_shorter(skb, ETH_IPV4_TCP_SIZE))

		goto out;



	eth = (void *)(long)skb->data;

	ip = (void *)(eth + 1);



out:

	return ip;

}



SEC("classifier/cls")

int main_prog(struct __sk_buff *skb)

{

	struct iphdr *ip = NULL;

	struct tcphdr *tcp;

	__u8 proto = 0;



	if (!(ip = get_iphdr(skb)))

		goto out;



	proto = ip->protocol;



	if (proto != IPPROTO_TCP)

		goto out;



	tcp = (void*)(ip + 1);

	if (tcp->dest != 0)

		goto out;

	if (!tcp)

		goto out;



	return tcp->urg_ptr;

out:

	return -1;

}

char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/verifier/ctx_skb.c

+42 −0
Original line number Diff line number Diff line
@@ -1089,3 +1089,45 @@ 
	.errstr_unpriv = "R1 leaks addr",

	.result = REJECT,

},

{

       "pkt > pkt_end taken check",

       .insns = {

       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,                //  0. r2 = *(u32 *)(r1 + data_end)

                   offsetof(struct __sk_buff, data_end)),

       BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1,                //  1. r4 = *(u32 *)(r1 + data)

                   offsetof(struct __sk_buff, data)),

       BPF_MOV64_REG(BPF_REG_3, BPF_REG_4),                    //  2. r3 = r4

       BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, 42),                  //  3. r3 += 42

       BPF_MOV64_IMM(BPF_REG_1, 0),                            //  4. r1 = 0

       BPF_JMP_REG(BPF_JGT, BPF_REG_3, BPF_REG_2, 2),          //  5. if r3 > r2 goto 8

       BPF_ALU64_IMM(BPF_ADD, BPF_REG_4, 14),                  //  6. r4 += 14

       BPF_MOV64_REG(BPF_REG_1, BPF_REG_4),                    //  7. r1 = r4

       BPF_JMP_REG(BPF_JGT, BPF_REG_3, BPF_REG_2, 1),          //  8. if r3 > r2 goto 10

       BPF_LDX_MEM(BPF_H, BPF_REG_2, BPF_REG_1, 9),            //  9. r2 = *(u8 *)(r1 + 9)

       BPF_MOV64_IMM(BPF_REG_0, 0),                            // 10. r0 = 0

       BPF_EXIT_INSN(),                                        // 11. exit

       },

       .result = ACCEPT,

       .prog_type = BPF_PROG_TYPE_SK_SKB,

},

{

       "pkt_end < pkt taken check",

       .insns = {

       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,                //  0. r2 = *(u32 *)(r1 + data_end)

                   offsetof(struct __sk_buff, data_end)),

       BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1,                //  1. r4 = *(u32 *)(r1 + data)

                   offsetof(struct __sk_buff, data)),

       BPF_MOV64_REG(BPF_REG_3, BPF_REG_4),                    //  2. r3 = r4

       BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, 42),                  //  3. r3 += 42

       BPF_MOV64_IMM(BPF_REG_1, 0),                            //  4. r1 = 0

       BPF_JMP_REG(BPF_JGT, BPF_REG_3, BPF_REG_2, 2),          //  5. if r3 > r2 goto 8

       BPF_ALU64_IMM(BPF_ADD, BPF_REG_4, 14),                  //  6. r4 += 14

       BPF_MOV64_REG(BPF_REG_1, BPF_REG_4),                    //  7. r1 = r4

       BPF_JMP_REG(BPF_JLT, BPF_REG_2, BPF_REG_3, 1),          //  8. if r2 < r3 goto 10

       BPF_LDX_MEM(BPF_H, BPF_REG_2, BPF_REG_1, 9),            //  9. r2 = *(u8 *)(r1 + 9)

       BPF_MOV64_IMM(BPF_REG_0, 0),                            // 10. r0 = 0

       BPF_EXIT_INSN(),                                        // 11. exit

       },

       .result = ACCEPT,

       .prog_type = BPF_PROG_TYPE_SK_SKB,

},

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