Re: [PATCH bpf-next v3 0/3] Allow variable offsets for syscall PTR_TO_CTX

[Puranjay Mohan <puranjay@kernel.org>]

Kumar Kartikeya Dwivedi <memxor@gmail.com> writes:

> Enable pointer modification with variable offsets accumulated in the
> register for PTR_TO_CTX for syscall programs where it won't be
> rewritten, and the context is user-supplied and checked against the max
> offset. See patches for details. Fixed offset support landed in [0].
>
> By combining this set with [0], examples like the one below should
> succeed verification now.
>
>   SEC("syscall")
>   int prog(void *ctx) {
> 	int *arr = ctx;
> 	int i;
>
> 	bpf_for(i, 0, 100)
> 		arr[i] *= i;
>
> 	return 0;
>   }
>
>   [0]: https://lore.kernel.org/bpf/20260227005725.1247305-1-memxor@gmail.com
>
> Changelog:
> ----------
> v2 -> v3
> v2: https://lore.kernel.org/bpf/20260318075133.1031781-1-memxor@gmail.com
>
>  * Prevent arg_type for KF_ARG_PTR_TO_CTX from applying to other cases
>    due to preceding fallthrough. (Gemini/Sashiko)
>
> v1 -> v2
> v1: https://lore.kernel.org/bpf/20260317111850.2107846-2-memxor@gmail.com
>
>  * Harden check_func_arg_reg_off check with ARG_PTR_TO_CTX.
>  * Add tests for unmodified ctx into tail calls.
>  * Squash unmodified ctx change into base commit.
>  * Add Reviewed-by's from Emil.
>
> Kumar Kartikeya Dwivedi (3):
>   bpf: Support variable offsets for syscall PTR_TO_CTX
>   selftests/bpf: Add syscall ctx variable offset tests
>   selftests/bpf: Test modified syscall ctx for ARG_PTR_TO_CTX
>
>  kernel/bpf/verifier.c                         |  67 ++--
>  .../selftests/bpf/prog_tests/verifier.c       |  34 +-
>  .../selftests/bpf/progs/verifier_ctx.c        | 356 +++++++++++++++---
>  .../bpf/progs/verifier_global_subprogs.c      |  95 ++++-
>  .../selftests/bpf/test_kmods/bpf_testmod.c    |   2 +-
>  5 files changed, 462 insertions(+), 92 deletions(-)
>
>
> base-commit: 77378dabb50f593c756d393d8eacb0b91b758863
> -- 
> 2.52.0

Acked-by: Puranjay Mohan <puranjay@kernel.org>

Thanks,
Puranjay