bpf: Varying offset access support for PTR_TO_BTF_ID pointers

Relax the requirements for reads like `p->arr[i].field`, where `p` is a
PTR_TO_BTF_ID, by allowing `i` to be a non-constant value.
This is useful for loops over arrays accessed from a PTR_TO_BTF_ID
when the verifier widens the loop induction variable.

Check that the access stays within array bounds based on the access
register's min and max bounds. Check that the access is aligned with
array elements using the register's `base` and `step`.

Technically, modify btf_struct_access() such that:
- it identifies `field` by walking BTF from the minimum offset
  (the register's reg_smin + static instruction offset);
- it remembers which arrays contain `field`;
- it checks that offsets `k * step` stay within the array
  and point to the same `field`;
- it does not check upper bounds for flexible arrays
  (as is already the case for constant-offset access).

Support for flexible arrays nested inside trailing struct members
(e.g. p->nested.data[i], with data declared as int data[]) is left
for future work.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261009-scev-minimal-rebase-v3-20-bcba9bc53ac9@gmail.com

0 files changed, 0 insertions, 0 deletions