57a09bf0a4
A BPF program is required to check the return register of a map_elem_lookup() call before accessing memory. The verifier keeps track of this by converting the type of the result register from PTR_TO_MAP_VALUE_OR_NULL to PTR_TO_MAP_VALUE after a conditional jump ensures safety. This check is currently exclusively performed for the result register 0. In the event the compiler reorders instructions, BPF_MOV64_REG instructions may be moved before the conditional jump which causes them to keep their type PTR_TO_MAP_VALUE_OR_NULL to which the verifier objects when the register is accessed: 0: (b7) r1 = 10 1: (7b) *(u64 *)(r10 -8) = r1 2: (bf) r2 = r10 3: (07) r2 += -8 4: (18) r1 = 0x59c00000 6: (85) call 1 7: (bf) r4 = r0 8: (15) if r0 == 0x0 goto pc+1 R0=map_value(ks=8,vs=8) R4=map_value_or_null(ks=8,vs=8) R10=fp 9: (7a) *(u64 *)(r4 +0) = 0 R4 invalid mem access 'map_value_or_null' This commit extends the verifier to keep track of all identical PTR_TO_MAP_VALUE_OR_NULL registers after a map_elem_lookup() by assigning them an ID and then marking them all when the conditional jump is observed. Signed-off-by: Thomas Graf <tgraf@suug.ch> Reviewed-by: Josef Bacik <jbacik@fb.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
103 lines
3.2 KiB
C
103 lines
3.2 KiB
C
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*/
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#ifndef _LINUX_BPF_VERIFIER_H
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#define _LINUX_BPF_VERIFIER_H 1
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#include <linux/bpf.h> /* for enum bpf_reg_type */
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#include <linux/filter.h> /* for MAX_BPF_STACK */
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/* Just some arbitrary values so we can safely do math without overflowing and
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* are obviously wrong for any sort of memory access.
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*/
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#define BPF_REGISTER_MAX_RANGE (1024 * 1024 * 1024)
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#define BPF_REGISTER_MIN_RANGE -(1024 * 1024 * 1024)
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struct bpf_reg_state {
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enum bpf_reg_type type;
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/*
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* Used to determine if any memory access using this register will
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* result in a bad access.
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*/
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u64 min_value, max_value;
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u32 id;
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union {
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/* valid when type == CONST_IMM | PTR_TO_STACK | UNKNOWN_VALUE */
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s64 imm;
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/* valid when type == PTR_TO_PACKET* */
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struct {
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u16 off;
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u16 range;
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};
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/* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
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* PTR_TO_MAP_VALUE_OR_NULL
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*/
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struct bpf_map *map_ptr;
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};
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};
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enum bpf_stack_slot_type {
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STACK_INVALID, /* nothing was stored in this stack slot */
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STACK_SPILL, /* register spilled into stack */
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STACK_MISC /* BPF program wrote some data into this slot */
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};
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#define BPF_REG_SIZE 8 /* size of eBPF register in bytes */
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/* state of the program:
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* type of all registers and stack info
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*/
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struct bpf_verifier_state {
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struct bpf_reg_state regs[MAX_BPF_REG];
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u8 stack_slot_type[MAX_BPF_STACK];
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struct bpf_reg_state spilled_regs[MAX_BPF_STACK / BPF_REG_SIZE];
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};
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/* linked list of verifier states used to prune search */
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struct bpf_verifier_state_list {
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struct bpf_verifier_state state;
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struct bpf_verifier_state_list *next;
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};
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struct bpf_insn_aux_data {
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enum bpf_reg_type ptr_type; /* pointer type for load/store insns */
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};
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#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
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struct bpf_verifier_env;
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struct bpf_ext_analyzer_ops {
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int (*insn_hook)(struct bpf_verifier_env *env,
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int insn_idx, int prev_insn_idx);
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};
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/* single container for all structs
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* one verifier_env per bpf_check() call
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*/
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struct bpf_verifier_env {
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struct bpf_prog *prog; /* eBPF program being verified */
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struct bpf_verifier_stack_elem *head; /* stack of verifier states to be processed */
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int stack_size; /* number of states to be processed */
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struct bpf_verifier_state cur_state; /* current verifier state */
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struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
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const struct bpf_ext_analyzer_ops *analyzer_ops; /* external analyzer ops */
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void *analyzer_priv; /* pointer to external analyzer's private data */
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struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
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u32 used_map_cnt; /* number of used maps */
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u32 id_gen; /* used to generate unique reg IDs */
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bool allow_ptr_leaks;
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bool seen_direct_write;
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bool varlen_map_value_access;
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struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
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};
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int bpf_analyzer(struct bpf_prog *prog, const struct bpf_ext_analyzer_ops *ops,
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void *priv);
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#endif /* _LINUX_BPF_VERIFIER_H */
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