On Thu, 2024-12-19 at 21:09 -0700, Daniel Xu wrote:
lgtm, but please see a note below.
[...]
> +/* Returns constant key value if possible, else negative error */
> +static s64 get_constant_map_key(struct bpf_verifier_env *env,
> + struct bpf_reg_state *key,
> + u32 key_size)
> +{
> + struct bpf_func_state *state = func(env, key);
> + struct bpf_reg_state *reg;
> + int slot, spi, off;
> + int spill_size = 0;
> + int zero_size = 0;
> + int stack_off;
> + int i, err;
> + u8 *stype;
> +
> + if (!env->bpf_capable)
> + return -EOPNOTSUPP;
> + if (key->type != PTR_TO_STACK)
> + return -EOPNOTSUPP;
> + if (!tnum_is_const(key->var_off))
> + return -EOPNOTSUPP;
> +
> + stack_off = key->off + key->var_off.value;
> + slot = -stack_off - 1;
> + spi = slot / BPF_REG_SIZE;
> + off = slot % BPF_REG_SIZE;
> + stype = state->stack[spi].slot_type;
> +
> + /* First handle precisely tracked STACK_ZERO */
> + for (i = off; i >= 0 && stype[i] == STACK_ZERO; i--)
> + zero_size++;
> + if (zero_size >= key_size)
> + return 0;
> +
> + /* Check that stack contains a scalar spill of expected size */
> + if (!is_spilled_scalar_reg(&state->stack[spi]))
> + return -EOPNOTSUPP;
> + for (i = off; i >= 0 && stype[i] == STACK_SPILL; i--)
> + spill_size++;
> + if (spill_size != key_size)
> + return -EOPNOTSUPP;
> +
> + reg = &state->stack[spi].spilled_ptr;
> + if (!tnum_is_const(reg->var_off))
> + /* Stack value not statically known */
> + return -EOPNOTSUPP;
> +
> + /* We are relying on a constant value. So mark as precise
> + * to prevent pruning on it.
> + */
> + bt_set_frame_slot(&env->bt, env->cur_state->curframe, spi);
I think env->cur_state->curframe is not always correct here.
It should be key->frameno, as key might point a few stack frames up.
> + err = mark_chain_precision_batch(env);
> + if (err < 0)
> + return err;
> +
> + return reg->var_off.value;
> +}
> +
> static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> struct bpf_call_arg_meta *meta,
> const struct bpf_func_proto *fn,
[...]
