[PATCH bpf-next v11 0/8] bpf: Extend BPF syscall with common attributes support

[Leon Hwang <leon.hwang@linux.dev>]

This patch series builds upon the discussion in
"[PATCH bpf-next v4 0/4] bpf: Improve error reporting for freplace attachment failure" [1].

This patch series introduces support for *common attributes* in the BPF
syscall, providing a unified mechanism for passing shared metadata across
all BPF commands, initially used by BPF_PROG_LOAD, BPF_BTF_LOAD, and
BPF_MAP_CREATE.

The initial set of common attributes includes:

1. 'log_buf': User-provided buffer for storing log output.
2. 'log_size': Size of the provided log buffer.
3. 'log_level': Verbosity level for logging.
4. 'log_true_size': Actual log size reported by kernel.

With this extension, the BPF syscall will be able to return meaningful
error messages (e.g., map creation failures), improving debuggability
and user experience.

Links:
[1] https://lore.kernel.org/bpf/20250224153352.64689-1-leon.hwang@linux.dev/

Changes:
v10 -> v11:
* Collect Acked-by from Andrii, thanks.
* Validate whether log_buf, log_size, and log_level are valid by reusing
  bpf_verifier_log_attr_valid() in patch #4 (per Andrii).
* v10: https://lore.kernel.org/bpf/20260211151115.78013-1-leon.hwang@linux.dev/

v9 -> v10:
* Collect Acked-by from Andrii, thanks.
* Address comments from Andrii:
  * Drop log NULL check in bpf_log_attr_finalize().
  * Return -EFAULT early in bpf_log_attr_finalize().
  * Validate whether log_buf, log_size, and log_level are set.
  * Keep log_buf, log_size, log_level, and user-pointer log_true_size in struct
    bpf_log_attr.
  * Make prog_load and btf_load work with the new struct bpf_log_attr.
  * Add comment to log_true_size of struct bpf_log_opts in libbpf.
* Address comment from Alexei:
  * Avoid using BPF_LOG_FIXED as log_level in tests.
* v9: https://lore.kernel.org/bpf/20260202144046.30651-1-leon.hwang@linux.dev/

v8 -> v9:
* Rework reporting 'log_true_size' for prog_load, btf_load, and map_create to
  simplify struct bpf_log_attr (per Alexei).
* v8: https://lore.kernel.org/bpf/20260126151409.52072-1-leon.hwang@linux.dev/

v7 -> v8:
* Return 0 when fd < 0 and errno != EFAULT in probe_sys_bpf_ext(), then simplify
  probe_bpf_syscall_common_attrs() (per Alexei and Andrii).
* v7: https://lore.kernel.org/bpf/20260123032445.125259-1-leon.hwang@linux.dev/

v6 -> v7:
* Return -errno when fd < 0 and errno != EFAULT in probe_sys_bpf_ext().
* Convert return value of probe_sys_bpf_ext() to bool in
  probe_bpf_syscall_common_attrs().
* Address comments from Andrii:
  * Drop the comment, and handle fd >= 0 case explicitly in
    probe_sys_bpf_ext().
  * Return an error when fd >= 0 in probe_sys_bpf_ext().
* v6: https://lore.kernel.org/bpf/20260120152424.40766-1-leon.hwang@linux.dev/

v5 -> v6:
* Address comments from Andrii:
  * Update some variables' name.
  * Drop unnecessary 'close(fd)' in libbpf.
  * Rename FEAT_EXTENDED_SYSCALL to FEAT_BPF_SYSCALL_COMMON_ATTRS with
    updated description in libbpf.
  * Use EINVAL instead of EUSERS, as EUSERS is not used in bpf yet.
  * Rename struct bpf_syscall_common_attr_opts to bpf_log_opts in libbpf.
  * Add 'OPTS_SET(log_opts, log_true_size, 0);' in libbpf's 'bpf_map_create()'.
* v5: https://lore.kernel.org/bpf/20260112145616.44195-1-leon.hwang@linux.dev/

v4 -> v5:
* Rework reporting 'log_true_size' for prog_load, btf_load, and map_create
  (per Alexei).
* v4: https://lore.kernel.org/bpf/20260106172018.57757-1-leon.hwang@linux.dev/

RFC v3 -> v4:
* Drop RFC.
* Address comments from Andrii:
  * Add parentheses in 'sys_bpf_ext()'.
  * Avoid creating new fd in 'probe_sys_bpf_ext()'.
  * Add a new struct to wrap log fields in libbpf.
* Address comments from Alexei:
  * Do not skip writing to user space when log_true_size is zero.
  * Do not use 'bool' arguments.
  * Drop the adding WARN_ON_ONCE()'s.
* v3: https://lore.kernel.org/bpf/20251002154841.99348-1-leon.hwang@linux.dev/

RFC v2 -> RFC v3:
* Rename probe_sys_bpf_extended to probe_sys_bpf_ext.
* Refactor reporting 'log_true_size' for prog_load.
* Refactor reporting 'btf_log_true_size' for btf_load.
* Add warnings for internal bugs in map_create.
* Check log_true_size in test cases.
* Address comment from Alexei:
  * Change kvzalloc/kvfree to kzalloc/kfree.
* Address comments from Andrii:
  * Move BPF_COMMON_ATTRS to 'enum bpf_cmd' alongside brief comment.
  * Add bpf_check_uarg_tail_zero() for extra checks.
  * Rename sys_bpf_extended to sys_bpf_ext.
  * Rename sys_bpf_fd_extended to sys_bpf_ext_fd.
  * Probe the new feature using NULL and -EFAULT.
  * Move probe_sys_bpf_ext to libbpf_internal.h and drop LIBBPF_API.
  * Return -EUSERS when log attrs are conflict between bpf_attr and
    bpf_common_attr.
  * Avoid touching bpf_vlog_init().
  * Update the reason messages in map_create.
  * Finalize the log using __cleanup().
  * Report log size to users.
  * Change type of log_buf from '__u64' to 'const char *' and cast type
    using ptr_to_u64() in bpf_map_create().
  * Do not return -EOPNOTSUPP when kernel doesn't support this feature
    in bpf_map_create().
  * Add log_level support for map creation for consistency.
* Address comment from Eduard:
  * Use common_attrs->log_level instead of BPF_LOG_FIXED.
* v2: https://lore.kernel.org/bpf/20250911163328.93490-1-leon.hwang@linux.dev/

RFC v1 -> RFC v2:
* Fix build error reported by test bot.
* Address comments from Alexei:
  * Drop new uapi for freplace.
  * Add common attributes support for prog_load and btf_load.
  * Add common attributes support for map_create.
* v1: https://lore.kernel.org/bpf/20250728142346.95681-1-leon.hwang@linux.dev/

Leon Hwang (8):
  bpf: Extend BPF syscall with common attributes support
  libbpf: Add support for extended BPF syscall
  bpf: Refactor reporting log_true_size for prog_load
  bpf: Add syscall common attributes support for prog_load
  bpf: Add syscall common attributes support for btf_load
  bpf: Add syscall common attributes support for map_create
  libbpf: Add syscall common attributes support for map_create
  selftests/bpf: Add tests to verify map create failure log

 include/linux/bpf.h                           |   4 +-
 include/linux/bpf_verifier.h                  |  15 ++
 include/linux/btf.h                           |   3 +-
 include/linux/syscalls.h                      |   3 +-
 include/uapi/linux/bpf.h                      |   8 +
 kernel/bpf/btf.c                              |  30 +---
 kernel/bpf/log.c                              |  89 +++++++++-
 kernel/bpf/syscall.c                          | 114 +++++++++---
 kernel/bpf/verifier.c                         |  17 +-
 tools/include/uapi/linux/bpf.h                |   8 +
 tools/lib/bpf/bpf.c                           |  52 +++++-
 tools/lib/bpf/bpf.h                           |  17 +-
 tools/lib/bpf/features.c                      |   8 +
 tools/lib/bpf/libbpf_internal.h               |   3 +
 .../selftests/bpf/prog_tests/map_init.c       | 166 ++++++++++++++++++
 15 files changed, 470 insertions(+), 67 deletions(-)

--
2.52.0