On Sat, Sep 19, 2020 at 10:03 PM Tony Ambardar <tony.ambardar@xxxxxxxxx> wrote: > > Hello, > > I've been experimenting with BPF and BTF on small, emebedded platforms > requiring cross-compilation to varying archs, word-sizes, and endianness. > These environments are not the most common for the majority of eBPF users, > and have exposed multiple problems with basic functionality. This patch > series addresses some of these issues. > > Enabling BTF support in the kernel can sometimes result in sysfs export > of /sys/kernel/btf/vmlinux as a zero-length file, which is still readable > and seen to leak non-zero kernel data. Patch #1 adds a sanity-check to > avoid this situation. > > Small systems commonly enable LD_DEAD_CODE_DATA_ELIMINATION, which causes > the .BTF section data to be incorrectly removed and can trigger the problem > above. Patch #2 preserves the BTF data. > > Even if BTF data is generated and embedded in the kernel, it may be encoded > as non-native endianness due to another bug [1] currently being worked on. > Patch #3 lets bpftool recognize the wrong BTF endianness rather than output > a confusing/misleading ELF header error message. > > Patches #1 and #2 were first developed for Linux 5.4.x and should be > backported if possible. Feedback and suggestions for improvement are > welcome! > > Thanks, > Tony > > [1] https://lore.kernel.org/bpf/CAPGftE8ipAacAnm9xMHFabXCL-XrCXGmOsX-Nsjvz9wnh3Zx-w@xxxxxxxxxxxxxx/ > > Tony Ambardar (3): > bpf: fix sysfs export of empty BTF section > bpf: prevent .BTF section elimination > libbpf: fix native endian assumption when parsing BTF > > include/asm-generic/vmlinux.lds.h | 2 +- > kernel/bpf/sysfs_btf.c | 6 +++--- > tools/lib/bpf/btf.c | 6 ++++++ > 3 files changed, 10 insertions(+), 4 deletions(-) > > -- > 2.25.1 > All fixes look good: Acked-by: Andrii Nakryiko <andriin@xxxxxx>
