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: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b6a1f7c..a28e09c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1172,6 +1172,70 @@
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 @@
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)