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bpf: verifier: add checks for BPF_ABS | BPF_IND instructions

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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: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov 2014-12-01 15:06:34 -08:00 committed by David S. Miller
parent f51a5e82ea
commit ddd872bc30
2 changed files with 69 additions and 2 deletions
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1
include/uapi/linux/bpf.h
View File

@ -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 */

70
kernel/bpf/verifier.c
View File

@ -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)