On 6/22/20 11:39 PM, Andrii Nakryiko wrote:
On Mon, Jun 22, 2020 at 5:38 PM Yonghong Song <yhs@xxxxxx> wrote:
The helper is used in tracing programs to cast a socket
pointer to a tcp6_sock pointer.
The return value could be NULL if the casting is illegal.
A new helper return type RET_PTR_TO_BTF_ID_OR_NULL is added
so the verifier is able to deduce proper return types for the helper.
Different from the previous BTF_ID based helpers,
the bpf_skc_to_tcp6_sock() argument can be several possible
btf_ids. More specifically, all possible socket data structures
with sock_common appearing in the first in the memory layout.
This patch only added socket types related to tcp and udp.
All possible argument btf_id and return value btf_id
for helper bpf_skc_to_tcp6_sock() are pre-calculcated and
cached. In the future, it is even possible to precompute
these btf_id's at kernel build time.
Acked-by: Martin KaFai Lau <kafai@xxxxxx>
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
Looks good to me as is, but see a few suggestions, they will probably
save me time at some point as well :)
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
include/linux/bpf.h | 12 +++++
include/uapi/linux/bpf.h | 9 +++-
kernel/bpf/btf.c | 1 +
kernel/bpf/verifier.c | 43 +++++++++++++-----
kernel/trace/bpf_trace.c | 2 +
net/core/filter.c | 80 ++++++++++++++++++++++++++++++++++
scripts/bpf_helpers_doc.py | 2 +
tools/include/uapi/linux/bpf.h | 9 +++-
8 files changed, 146 insertions(+), 12 deletions(-)
[...]
@@ -4815,6 +4826,18 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
regs[BPF_REG_0].type = PTR_TO_MEM_OR_NULL;
regs[BPF_REG_0].id = ++env->id_gen;
regs[BPF_REG_0].mem_size = meta.mem_size;
+ } else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL) {
+ int ret_btf_id;
+
+ mark_reg_known_zero(env, regs, BPF_REG_0);
+ regs[BPF_REG_0].type = PTR_TO_BTF_ID_OR_NULL;
+ ret_btf_id = *fn->ret_btf_id;
might be a good idea to check fb->ret_btf_id for NULL and print a
warning + return -EFAULT. It's not supposed to happen on properly
configured kernel, but during development this will save a bunch of
time and frustration for next person trying to add something with
RET_PTR_TO_BTF_ID_OR_NULL.
I would like prefer to delay this with current code. Otherwise,
it gives an impression fn->ret_btf_id might be NULL and it is
actually never NULL. We can add NULL check if the future change
requires it. I am not sure what the future change could be,
but you need some way to get the return btf_id, the above is
one of them.
+ if (ret_btf_id == 0) {
This also has to be struct/union (after typedef/mods stripping, of
course). Or are there other cases?
This is an "int". The func_proto difinition is below:
int *ret_btf_id; /* return value btf_id */
+ verbose(env, "invalid return type %d of func %s#%d\n",
+ fn->ret_type, func_id_name(func_id), func_id);
+ return -EINVAL;
+ }
+ regs[BPF_REG_0].btf_id = ret_btf_id;
} else {
verbose(env, "unknown return type %d of func %s#%d\n",
fn->ret_type, func_id_name(func_id), func_id);
[...]
+void init_btf_sock_ids(struct btf *btf)
+{
+ int i, btf_id;
+
+ for (i = 0; i < MAX_BTF_SOCK_TYPE; i++) {
+ btf_id = btf_find_by_name_kind(btf, bpf_sock_types[i],
+ BTF_KIND_STRUCT);
+ if (btf_id > 0)
+ btf_sock_ids[i] = btf_id;
+ }
+}
This will hopefully go away with Jiri's work on static BTF IDs, right?
So looking forward to that :)
Yes. That's the plan.
+
+static bool check_arg_btf_id(u32 btf_id, u32 arg)
+{
+ int i;
+
+ /* only one argument, no need to check arg */
+ for (i = 0; i < MAX_BTF_SOCK_TYPE; i++)
+ if (btf_sock_ids[i] == btf_id)
+ return true;
+ return false;
+}
+
[...]
