[bpf-next,v2,0/2] Implement formatted output helpers with bstr_printf

Message

Florent Revest April 27, 2021, 5:43 p.m. UTC

BPF's formatted output helpers are currently implemented with
snprintf-like functions which use variadic arguments. The types of all
arguments need to be known at compilation time. BPF_CAST_FMT_ARG casts
all arguments to the size they should be (known at runtime), but the C
type promotion rules cast them back to u64s. On 32 bit architectures,
this can cause misaligned va_lists and generate mangled output.

This series refactors these helpers to avoid variadic arguments. It uses
a "binary printf" instead, where arguments are passed in a buffer
constructed at runtime.

---
Changes in v2:
- Reworded the second patch's description to better describe how
  arguments get mangled on 32 bit architectures

Florent Revest (2):
  seq_file: Add a seq_bprintf function
  bpf: Implement formatted output helpers with bstr_printf

 fs/seq_file.c            |  18 ++++
 include/linux/bpf.h      |  22 +----
 include/linux/seq_file.h |   4 +
 init/Kconfig             |   1 +
 kernel/bpf/helpers.c     | 188 +++++++++++++++++++++------------------
 kernel/bpf/verifier.c    |   2 +-
 kernel/trace/bpf_trace.c |  34 +++----
 7 files changed, 137 insertions(+), 132 deletions(-)