Commit 728ff167910e ("libbpf: Add gating for arena globals relocation feature")
adds a feature gate check that loads a map and BPF program to
test the running kernel supports large direct offsets for LDIMM64
instructions. This check is currently used to calculate arena symbol
offsets during bpf_object__collect_relos, itself called by
bpf_object_open.
However, the program calling bpf_object_open may not have the permissions to
load maps and programs. This is the case with the BPF selftests, where
bpftool is invoked at compilation time during skeleton generation. This
causes errors as the feature gate unexpectedly fails with -EPERM.
Avoid this by moving all the use of the FEAT_LDIMM64_FULL_RANGE_OFF feature gate
to BPF object preparation time instead.
Fixes: 728ff167910e ("libbpf: Add gating for arena globals relocation feature")
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260217204345.548648-3-emil@etsalapatis.com
Commit 728ff167910e uses a PROG_TYPE_TRACEPOINT BPF test program to
check whether the running kernel supports large LDIMM64 offsets. The
feature gate incorrectly assumes that the program will fail at
verification time with one of two messages, depending on whether the
feature is supported by the running kernel. However,
PROG_TYPE_TRACEPOINT programs may fail to load before verification even
starts, e.g., if the shell does not have the appropriate capabilities.
Use a BPF_PROG_TYPE_SOCKET_FILTER program for the feature gate instead.
Also fix two minor issues. First, ensure the log buffer for the test is
initialized: Failing program load before verification led to libbpf dumping
uninitialized data to stdout. Also, ensure that close() is only called
for program_fd in the probe if the program load actually succeeded. The
call was currently failing silently with -EBADF most of the time.
Fixes: 728ff167910e ("libbpf: Add gating for arena globals relocation feature")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260217204345.548648-2-emil@etsalapatis.com
Add feature gating for the arena globals relocation introduced in
commit c1f61171d44b. The commit depends on a previous commit in the
same patchset that is absent from older kernels
(12a1fe6e12db "bpf/verifier: Do not limit maximum direct offset into arena map").
Without this commit, arena globals relocation with arenas >= 512MiB
fails to load and breaks libbpf's backwards compatibility.
Introduce a libbpf feature to check whether the running kernel allows for
full range ldimm64 offset, and only relocate arena globals if it does.
Fixes: c1f61171d44b ("libbpf: Move arena globals to the end of the arena")
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260210184532.255475-1-emil@etsalapatis.com
Arena globals are currently placed at the beginning of the arena
by libbpf. This is convenient, but prevents users from reserving
guard pages in the beginning of the arena to identify NULL pointer
dereferences. Adjust the load logic to place the globals at the
end of the arena instead.
Also modify bpftool to set the arena pointer in the program's BPF
skeleton to point to the globals. Users now call bpf_map__initial_value()
to find the beginning of the arena mapping and use the arena pointer
in the skeleton to determine which part of the mapping holds the
arena globals and which part is free.
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20251216173325.98465-5-emil@etsalapatis.com
The symbols' relocation offsets in BPF are stored in an int field,
but cannot actually be negative. When in the next patch libbpf relocates
globals to the end of the arena, it is also possible to have valid
offsets > 2GiB that are used to calculate the final relo offsets.
Avoid accidentally interpreting large offsets as negative by turning
the sym_off field unsigned.
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20251216173325.98465-4-emil@etsalapatis.com
Emil Tsalapatis