On Sun, Aug 7, 2022 at 10:51 AM Yonghong Song <yhs@xxxxxx> wrote: > > Tejun reported a bpf program kfunc return value mis-handling which > may cause incorrect result. If the kfunc return value is boolean > or u8, the bpf program produce incorrect results. > > The main reason is due to mismatch of return value expectation between > native architecture and bpf. For example, for x86_64, if a kfunc > returns a u8, the kfunc returns 64-bit %rax, the top 56 bits might > be garbage. This is okay if the caller is x86_64 as the caller can > use special instruction to access lower 8-bit register %al. But this > will cause a problem for bpf program since bpf program assumes > the whole r0 register should contain correct value. > This patch set fixed the issue by doing necessary zero/sign extension > for the kfunc return value to meet bpf requirement. > > For the rest of patches, Patch 1 is a preparation patch. Patch 2 > implemented kernel support to perform necessary zero/sign extension > for kfunc return value. Patch 3 added two tests, one with return type > u8 and another with s16. > > Yonghong Song (3): > bpf: Always return corresponding btf_type in __get_type_size() > bpf: Perform necessary sign/zero extension for kfunc return values > selftests/bpf: Add tests with u8/s16 kfunc return types > > include/linux/bpf.h | 2 ++ > kernel/bpf/btf.c | 18 +++++++--- > kernel/bpf/verifier.c | 35 +++++++++++++++++-- > net/bpf/test_run.c | 12 +++++++ > .../selftests/bpf/prog_tests/kfunc_call.c | 10 ++++++ > .../selftests/bpf/progs/kfunc_call_test.c | 32 +++++++++++++++++ > 6 files changed, 102 insertions(+), 7 deletions(-) > > -- > 2.30.2 > LGTM. Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
