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authorAlexei Starovoitov <ast@fb.com>2016-05-05 19:49:11 -0700
committerDavid S. Miller <davem@davemloft.net>2016-05-06 16:01:54 -0400
commit735b433397ea2f97d59240cbe4ea770aa7c88eef (patch)
treec2caeca835dc4a72ee04652e37274c98d4ad88eb /kernel/bpf
parent969bf05eb3cedd5a8d4b7c346a85c2ede87a6d6d (diff)
downloadlinux-sh-735b433397ea2f97d59240cbe4ea770aa7c88eef.tar.gz
bpf: improve verifier state equivalence
since UNKNOWN_VALUE type is weaker than CONST_IMM we can un-teach verifier its recognition of constants in conditional branches without affecting safety. Ex: if (reg == 123) { .. here verifier was marking reg->type as CONST_IMM instead keep reg as UNKNOWN_VALUE } Two verifier states with UNKNOWN_VALUE are equivalent, whereas CONST_IMM_X != CONST_IMM_Y, since CONST_IMM is used for stack range verification and other cases. So help search pruning by marking registers as UNKNOWN_VALUE where possible instead of CONST_IMM. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel/bpf')
-rw-r--r--kernel/bpf/verifier.c23
1 files changed, 3 insertions, 20 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6338c61fc2a1..84bff68cf80e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1704,12 +1704,11 @@ static int check_cond_jmp_op(struct verifier_env *env,
*/
regs[insn->dst_reg].type = PTR_TO_MAP_VALUE;
/* branch targer cannot access it, since reg == 0 */
- other_branch->regs[insn->dst_reg].type = CONST_IMM;
- other_branch->regs[insn->dst_reg].imm = 0;
+ mark_reg_unknown_value(other_branch->regs,
+ insn->dst_reg);
} else {
other_branch->regs[insn->dst_reg].type = PTR_TO_MAP_VALUE;
- regs[insn->dst_reg].type = CONST_IMM;
- regs[insn->dst_reg].imm = 0;
+ mark_reg_unknown_value(regs, insn->dst_reg);
}
} else if (BPF_SRC(insn->code) == BPF_X && opcode == BPF_JGT &&
dst_reg->type == PTR_TO_PACKET &&
@@ -1718,22 +1717,6 @@ static int check_cond_jmp_op(struct verifier_env *env,
} else if (is_pointer_value(env, insn->dst_reg)) {
verbose("R%d pointer comparison prohibited\n", insn->dst_reg);
return -EACCES;
- } else if (BPF_SRC(insn->code) == BPF_K &&
- (opcode == BPF_JEQ || opcode == BPF_JNE)) {
-
- if (opcode == BPF_JEQ) {
- /* detect if (R == imm) goto
- * and in the target state recognize that R = imm
- */
- other_branch->regs[insn->dst_reg].type = CONST_IMM;
- other_branch->regs[insn->dst_reg].imm = insn->imm;
- } else {
- /* detect if (R != imm) goto
- * and in the fall-through state recognize that R = imm
- */
- regs[insn->dst_reg].type = CONST_IMM;
- regs[insn->dst_reg].imm = insn->imm;
- }
}
if (log_level)
print_verifier_state(&env->cur_state);