[PATCH v5 bpf-next 2/4] bpf: Consider all mem_types compatible for map_{key,value} args

Dave Marchevsky
2022-10-20T16:07:39Z

After the previous patch, which added PTR_TO_MEM | MEM_ALLOC type
map_key_value_types, the only difference between map_key_value_types and
mem_types sets is PTR_TO_BUF and PTR_TO_MEM, which are in the latter set
but not the former.

Helpers which expect ARG_PTR_TO_MAP_KEY or ARG_PTR_TO_MAP_VALUE
already effectively expect a valid blob of arbitrary memory that isn't
necessarily explicitly associated with a map. When validating a
PTR_TO_MAP_{KEY,VALUE} arg, the verifier expects meta->map_ptr to have
already been set, either by an earlier ARG_CONST_MAP_PTR arg, or custom
logic like that in process_timer_func or process_kptr_func.

So let's get rid of map_key_value_types and just use mem_types for those
args.

This has the effect of adding PTR_TO_BUF and PTR_TO_MEM to the set of
compatible types for ARG_PTR_TO_MAP_KEY and ARG_PTR_TO_MAP_VALUE.

PTR_TO_BUF is used by various bpf_iter implementations to represent a
chunk of valid r/w memory in ctx args for iter prog.

PTR_TO_MEM is used by networking, tracing, and ringbuf helpers to
represent a chunk of valid memory. The PTR_TO_MEM | MEM_ALLOC
type added in previous commmit is specific to ringbuf helpers.
Presence or absence of MEM_ALLOC doesn't change the validity of using
PTR_TO_MEM as a map_{key,val} input.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
---
v1 -> v5: lore.kernel.org/bpf/20220912101106.2765921-2-davemarchevsky@fb.com

* This patch was dropped in v2 as I had no concrete usecase for
PTR_TO_BUF and PTR_TO_MEM w/o MEM_ALLOC. Andrii encouraged me to
re-add the patch as we both share desire to eventually cleanup all
these separate "valid chunk of memory" types. Starting to treat them
similarly is a good step in that direction.
* A usecase for PTR_TO_BUF is now demonstrated in patch 4 of this
series.
* PTR_TO_MEM w/o MEM_ALLOC is returned by bpf_{this,per}_cpu_ptr
helpers via RET_PTR_TO_MEM_OR_BTF_ID, but in both cases the return
type is also tagged MEM_RDONLY, which map helpers don't currently
accept (see patch 4 summary). So no selftest for this specific
case is added in the series, but by logic in this patch summary
there's no reason to treat it differently.

kernel/bpf/verifier.c | 15 ++-------------
1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 97351ae3e7a7..ddc1452cf023 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5634,17 +5634,6 @@ struct bpf_reg_types {
u32 *btf_id;
};

-static const struct bpf_reg_types map_key_value_types = {
- .types = {
- PTR_TO_STACK,
- PTR_TO_PACKET,
- PTR_TO_PACKET_META,
- PTR_TO_MAP_KEY,
- PTR_TO_MAP_VALUE,
- PTR_TO_MEM | MEM_ALLOC,
- },
-};
-
static const struct bpf_reg_types sock_types = {
.types = {
PTR_TO_SOCK_COMMON,
@@ -5711,8 +5700,8 @@ static const struct bpf_reg_types dynptr_types = {
};

static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
- [ARG_PTR_TO_MAP_KEY] = &map_key_value_types,
- [ARG_PTR_TO_MAP_VALUE] = &map_key_value_types,
+ [ARG_PTR_TO_MAP_KEY] = &mem_types,
+ [ARG_PTR_TO_MAP_VALUE] = &mem_types,
[ARG_CONST_SIZE] = &scalar_types,
[ARG_CONST_SIZE_OR_ZERO] = &scalar_types,
[ARG_CONST_ALLOC_SIZE_OR_ZERO] = &scalar_types,
--
2.30.2