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bpf: properly reset caller saved regs after helper call and ld_abs/ind

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Currently, after performing helper calls, we clear all caller saved
registers, that is r0 - r5 and fill r0 depending on struct bpf_func_proto
specification. The way we reset these regs can affect pruning decisions
in later paths, since we only reset register's imm to 0 and type to
NOT_INIT. However, we leave out clearing of other variables such as id,
min_value, max_value, etc, which can later on lead to pruning mismatches
due to stale data.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Daniel Borkmann 2017-05-25 01:05:06 +02:00 committed by David S. Miller
parent 1ad2f5838d
commit a9789ef9af
1 changed files with 16 additions and 21 deletions
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37
kernel/bpf/verifier.c
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@ -463,19 +463,22 @@ static const int caller_saved[CALLER_SAVED_REGS] = {
BPF_REG_0, BPF_REG_1, BPF_REG_2, BPF_REG_3, BPF_REG_4, BPF_REG_5
};
static void mark_reg_not_init(struct bpf_reg_state *regs, u32 regno)
{
BUG_ON(regno >= MAX_BPF_REG);
memset(&regs[regno], 0, sizeof(regs[regno]));
regs[regno].type = NOT_INIT;
regs[regno].min_value = BPF_REGISTER_MIN_RANGE;
regs[regno].max_value = BPF_REGISTER_MAX_RANGE;
}
static void init_reg_state(struct bpf_reg_state *regs)
{
int i;
for (i = 0; i < MAX_BPF_REG; i++) {
regs[i].type = NOT_INIT;
regs[i].imm = 0;
regs[i].min_value = BPF_REGISTER_MIN_RANGE;
regs[i].max_value = BPF_REGISTER_MAX_RANGE;
regs[i].min_align = 0;
regs[i].aux_off = 0;
regs[i].aux_off_align = 0;
}
for (i = 0; i < MAX_BPF_REG; i++)
mark_reg_not_init(regs, i);
/* frame pointer */
regs[BPF_REG_FP].type = FRAME_PTR;
@ -1346,7 +1349,6 @@ static int check_call(struct bpf_verifier_env *env, int func_id, int insn_idx)
struct bpf_verifier_state *state = &env->cur_state;
const struct bpf_func_proto *fn = NULL;
struct bpf_reg_state *regs = state->regs;
struct bpf_reg_state *reg;
struct bpf_call_arg_meta meta;
bool changes_data;
int i, err;
@ -1413,11 +1415,8 @@ static int check_call(struct bpf_verifier_env *env, int func_id, int insn_idx)
}
/* reset caller saved regs */
for (i = 0; i < CALLER_SAVED_REGS; i++) {
reg = regs + caller_saved[i];
reg->type = NOT_INIT;
reg->imm = 0;
}
for (i = 0; i < CALLER_SAVED_REGS; i++)
mark_reg_not_init(regs, caller_saved[i]);
/* update return register */
if (fn->ret_type == RET_INTEGER) {
@ -2445,7 +2444,6 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
{
struct bpf_reg_state *regs = env->cur_state.regs;
u8 mode = BPF_MODE(insn->code);
struct bpf_reg_state *reg;
int i, err;
if (!may_access_skb(env->prog->type)) {
@ -2478,11 +2476,8 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
}
/* 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;
}
for (i = 0; i < CALLER_SAVED_REGS; i++)
mark_reg_not_init(regs, caller_saved[i]);
/* mark destination R0 register as readable, since it contains
* the value fetched from the packet