bpf: generalize dynptr_get_spi to be usable for iters

Generalize the logic of fetching special stack slot object state using
spi (stack slot index). This will be used by STACK_ITER logic next.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230302235015.2044271-12-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d95975c..c4151c9 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -710,32 +710,38 @@ static bool is_spi_bounds_valid(struct bpf_func_state *state, int spi, int nr_sl
        return spi - nr_slots + 1 >= 0 && spi < allocated_slots;
 }
 
-static int dynptr_get_spi(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+static int stack_slot_obj_get_spi(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+                                 const char *obj_kind, int nr_slots)
 {
        int off, spi;
 
        if (!tnum_is_const(reg->var_off)) {
-               verbose(env, "dynptr has to be at a constant offset\n");
+               verbose(env, "%s has to be at a constant offset\n", obj_kind);
                return -EINVAL;
        }
 
        off = reg->off + reg->var_off.value;
        if (off % BPF_REG_SIZE) {
-               verbose(env, "cannot pass in dynptr at an offset=%d\n", off);
+               verbose(env, "cannot pass in %s at an offset=%d\n", obj_kind, off);
                return -EINVAL;
        }
 
        spi = __get_spi(off);
-       if (spi < 1) {
-               verbose(env, "cannot pass in dynptr at an offset=%d\n", off);
+       if (spi + 1 < nr_slots) {
+               verbose(env, "cannot pass in %s at an offset=%d\n", obj_kind, off);
                return -EINVAL;
        }
 
-       if (!is_spi_bounds_valid(func(env, reg), spi, BPF_DYNPTR_NR_SLOTS))
+       if (!is_spi_bounds_valid(func(env, reg), spi, nr_slots))
                return -ERANGE;
        return spi;
 }
 
+static int dynptr_get_spi(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+{
+       return stack_slot_obj_get_spi(env, reg, "dynptr", BPF_DYNPTR_NR_SLOTS);
+}
+
 static const char *kernel_type_name(const struct btf* btf, u32 id)
 {
        return btf_name_by_offset(btf, btf_type_by_id(btf, id)->name_off);