[PATCH bpf-next v4 0/7] Allow variable offsets for syscall PTR_TO_CTX

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

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:
----------
v3 -> v4
v3: https://lore.kernel.org/bpf/20260318103526.2590079-1-memxor@gmail.com

 * Drop comment around describing choice of fixed or variable offsets. (Eduard)
 * Simplify offset adjustment for different cases. (Eduard)
 * Add PTR_TO_CTX case in __check_mem_access(). (Eduard)
 * Drop aligned access constraint from syscall_prog_is_valid_access().
 * Wrap naked checks for BPF_PROG_TYPE_SYSCALL in a utility function. (Eduard)
 * Split tests into separate clean up and addition patches. (Eduard)
 * Remove CAP_SYS_ADMIN changes. (Eduard)
 * Enable unaligned access to syscall ctx, add tests.
 * Add more tests for various corner cases.
 * Add acks. (Puranjay, Mykyta)

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 (7):
  bpf: Support variable offsets for syscall PTR_TO_CTX
  bpf: Enable unaligned accesses for syscall ctx
  selftests/bpf: Convert ctx tests from ASM to C
  selftests/bpf: Add syscall ctx variable offset tests
  selftests/bpf: Test modified syscall ctx for ARG_PTR_TO_CTX
  selftests/bpf: Add tests for unaligned syscall ctx accesses
  selftests/bpf: Add tests for syscall ctx accesses beyond U16_MAX

 kernel/bpf/syscall.c                          |   3 +-
 kernel/bpf/verifier.c                         | 104 +--
 .../selftests/bpf/prog_tests/verifier.c       |   2 +-
 .../selftests/bpf/progs/verifier_ctx.c        | 591 ++++++++++++++++--
 .../bpf/progs/verifier_global_subprogs.c      |  95 ++-
 .../selftests/bpf/test_kmods/bpf_testmod.c    |   2 +-
 6 files changed, 704 insertions(+), 93 deletions(-)


base-commit: 0eeb0094ba0321f0927806857b5f01c1577bc245
-- 
2.52.0