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Commit ddd872bc authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

bpf: verifier: add checks for BPF_ABS | BPF_IND instructions 



introduce program type BPF_PROG_TYPE_SOCKET_FILTER that is used
for attaching programs to sockets where ctx == skb.

add verifier checks for ABS/IND instructions which can only be seen
in socket filters, therefore the check:
  if (env->prog->aux->prog_type != BPF_PROG_TYPE_SOCKET_FILTER)
    verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n");

Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f51a5e82

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -117,6 +117,7 @@ enum bpf_map_type { 


enum bpf_prog_type {

	BPF_PROG_TYPE_UNSPEC,

	BPF_PROG_TYPE_SOCKET_FILTER,

};



/* flags for BPF_MAP_UPDATE_ELEM command */

kernel/bpf/verifier.c

+68 −2
Original line number Diff line number Diff line
@@ -1172,6 +1172,70 @@ static int check_ld_imm(struct verifier_env *env, struct bpf_insn *insn) 
	return 0;

}



/* verify safety of LD_ABS|LD_IND instructions:

 * - they can only appear in the programs where ctx == skb

 * - since they are wrappers of function calls, they scratch R1-R5 registers,

 *   preserve R6-R9, and store return value into R0

 *

 * Implicit input:

 *   ctx == skb == R6 == CTX

 *

 * Explicit input:

 *   SRC == any register

 *   IMM == 32-bit immediate

 *

 * Output:

 *   R0 - 8/16/32-bit skb data converted to cpu endianness

 */

static int check_ld_abs(struct verifier_env *env, struct bpf_insn *insn)

{

	struct reg_state *regs = env->cur_state.regs;

	u8 mode = BPF_MODE(insn->code);

	struct reg_state *reg;

	int i, err;



	if (env->prog->aux->prog_type != BPF_PROG_TYPE_SOCKET_FILTER) {

		verbose("BPF_LD_ABS|IND instructions are only allowed in socket filters\n");

		return -EINVAL;

	}



	if (insn->dst_reg != BPF_REG_0 || insn->off != 0 ||

	    (mode == BPF_ABS && insn->src_reg != BPF_REG_0)) {

		verbose("BPF_LD_ABS uses reserved fields\n");

		return -EINVAL;

	}



	/* check whether implicit source operand (register R6) is readable */

	err = check_reg_arg(regs, BPF_REG_6, SRC_OP);

	if (err)

		return err;



	if (regs[BPF_REG_6].type != PTR_TO_CTX) {

		verbose("at the time of BPF_LD_ABS|IND R6 != pointer to skb\n");

		return -EINVAL;

	}



	if (mode == BPF_IND) {

		/* check explicit source operand */

		err = check_reg_arg(regs, insn->src_reg, SRC_OP);

		if (err)

			return err;

	}



	/* reset caller saved regs to unreadable */

	for (i = 0; i < CALLER_SAVED_REGS; i++) {

		reg = regs + caller_saved[i];

		reg->type = NOT_INIT;

		reg->imm = 0;

	}



	/* mark destination R0 register as readable, since it contains

	 * the value fetched from the packet

	 */

	regs[BPF_REG_0].type = UNKNOWN_VALUE;

	return 0;

}



/* non-recursive DFS pseudo code

 * 1  procedure DFS-iterative(G,v):

 * 2      label v as discovered
@@ -1677,8 +1741,10 @@ static int do_check(struct verifier_env *env) 
			u8 mode = BPF_MODE(insn->code);



			if (mode == BPF_ABS || mode == BPF_IND) {

				verbose("LD_ABS is not supported yet\n");

				return -EINVAL;

				err = check_ld_abs(env, insn);

				if (err)

					return err;



			} else if (mode == BPF_IMM) {

				err = check_ld_imm(env, insn);

				if (err)