From: Yuan Chen <[email protected]>
When BPF programs reference global variables (e.g., struct_ops
programs with global data), libbpf creates internal ARRAY maps to
back them. This depends on FEAT_GLOBAL_DATA, which is gated by
feature probes that load test programs (SOCKET_FILTER, KPROBE, etc.)
into the kernel.
In a user namespace with an implicit BPF token, two problems arise:
1. bpf_object__probe_loading() passes the token fd to test program
loads. When the token's allowed program type mask excludes the
probe types, the kernel drops the token reference, causing
subsequent struct_ops loads to fail because the token object
has been released.
2. The feature probe framework uses probe_fd() which returns 0 on
BPF syscall failure, and feat_supported() interprets ret==0 as
"feature absent". The token rescue path only handles ret<0,
so the probe failure is incorrectly cached as a missing feature,
and internal maps for global data are never created.
Together, these cause struct_ops programs referencing global data
to fail verification with "fd X is not pointing to valid bpf_map".
This series fixes both issues:
Patch 1: Skip bpf_object__probe_loading() entirely when a BPF
token is present. Token creation itself proves the
kernel BPF subsystem works.
Patch 2: Add BPF_MAP_TYPE_ARRAY to the token delegation mask for
struct_ops selftests so global data maps can be created.
Patch 3: Fix probe_fd() to return the actual error code instead
of 0 on failure, and add a token-aware rescue path in
feat_supported() for ret<0 cases.
Reproducible by running the implicit token tests with struct_ops in a
user namespace (tools/testing/selftests/bpf, test_progs -t token).
v2:
- Replace the workaround of granting SOCKET_FILTER/KPROBE permissions
in the token with a proper fix at the feature probe level in libbpf.
- probe_fd() now returns the actual error code on failure instead of
0, allowing feat_supported() to distinguish probe errors from
genuine feature absence.
- Add token_fd rescue path in feat_supported() for ret<0 cases.
Yuan Chen (3):
libbpf: Skip bpf_object__probe_loading() when BPF token is in use
selftests/bpf: Add ARRAY map type to token tests that use struct_ops
global data
libbpf: fix feature probe failures for implicit BPF tokens
tools/lib/bpf/features.c | 23 +++++++++++++++++--
tools/lib/bpf/libbpf.c | 10 +++-----
.../testing/selftests/bpf/prog_tests/token.c | 6 ++---
3 files changed, 27 insertions(+), 12 deletions(-)
--
2.54.0
