[PATCH bpf-next 00/11] RFC: Make check_func_arg table driven

[Lorenz Bauer <lmb@cloudflare.com>]

This is what happened when I got sidetracked from my work on sockmap
bpf_iter support [1]. For that I wanted to allow passing a BTF pointer
to functions expecting a PTR_TO_SOCKET. At first it wasn't at all
obvious to me how to add this to check_func_arg, so I started refactoring
the function bit by bit. This RFC series is the result of that.

Note: this series is based on top of sockmap iterator, hence the RFC status.

Currently, check_func_arg has this pretty gnarly if statement that
compares the valid arg_type with the actualy reg_type. Sprinkled
in-between are checks for register_is_null, to short circuit these
tests if we're dealing with a nullable arg_type. There is also some
code for later bounds / access checking hidden away in there.

This series of patches refactors the function into something like this:

   if (reg_is_null && arg_type_is_nullable)
     skip type checking

   do type checking, including BTF validation

   do bounds / access checking

The type checking is now table driven, which makes it easy to extend
the acceptable types. Maybe more importantly, using a table makes it
easy to provide more helpful verifier output (see the last patch).

I realise there are quite a few patches here. The most interesting
ones are #5 where I introduce a btf_id_set for each helper arg,
#10 where I simplify the nullable type checking and finally #11
where I add the table of compatible types.

There are some more simplifications that we could do that could get
rid of resolve_map_arg_type, but the series is already too long.

Martin: you said that you're working on extending PTR_TO_SOCK_COMMON,
would this series help you with that?

1: https://lore.kernel.org/bpf/20200904095904.612390-1-lmb@cloudflare.com/T/#t

Lorenz Bauer (11):
  btf: Fix BTF_SET_START_GLOBAL macro
  btf: add a global set of valid BTF socket ids
  btf: make btf_set_contains take a const pointer
  bpf: check scalar or invalid register in check_helper_mem_access
  bpf: allow specifying a set of BTF IDs for helper arguments
  bpf: make reference tracking in check_func_arg generic
  bpf: always check access to PTR_TO_CTX regardless of arg_type
  bpf: set meta->raw_mode for pointers to memory closer to it's use
  bpf: check ARG_PTR_TO_SPINLOCK register type in check_func_arg
  bpf: hoist type checking for nullable arg types
  bpf: use a table to drive helper arg type checks

 include/linux/bpf.h            |  25 ++-
 include/linux/btf_ids.h        |   7 +-
 kernel/bpf/bpf_inode_storage.c |   8 +-
 kernel/bpf/btf.c               |  24 +--
 kernel/bpf/stackmap.c          |   5 +-
 kernel/bpf/verifier.c          | 355 ++++++++++++++++++---------------
 kernel/trace/bpf_trace.c       |  15 +-
 net/core/bpf_sk_storage.c      |  10 +-
 net/core/filter.c              |  38 ++--
 net/ipv4/bpf_tcp_ca.c          |  24 +--
 tools/include/linux/btf_ids.h  |   7 +-
 11 files changed, 269 insertions(+), 249 deletions(-)

-- 
2.25.1