Messages in this thread | | | Subject | Re: [PATCH bpf v2 3/5] libbpf: Skip adjust mem size for load pointer in 32-bit arch in CO_RE | From | Yang Jihong <> | Date | Tue, 8 Nov 2022 10:44:59 +0800 |
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Hello,
On 2022/11/8 9:22, Andrii Nakryiko wrote: > On Mon, Nov 7, 2022 at 1:23 AM Yang Jihong <yangjihong1@huawei.com> wrote: >> >> bpf_core_patch_insn modifies load's mem size from 8 bytes to 4 bytes. >> As a result, the bpf check fails, we need to skip adjust mem size to fit >> the verifier. >> >> Signed-off-by: Yang Jihong <yangjihong1@huawei.com> >> --- >> tools/lib/bpf/libbpf.c | 34 +++++++++++++++++++++++++++++----- >> 1 file changed, 29 insertions(+), 5 deletions(-) >> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c >> index 184ce1684dcd..e1c21b631a0b 100644 >> --- a/tools/lib/bpf/libbpf.c >> +++ b/tools/lib/bpf/libbpf.c >> @@ -5634,6 +5634,28 @@ static int bpf_core_resolve_relo(struct bpf_program *prog, >> targ_res); >> } >> >> +static bool >> +bpf_core_patch_insn_skip(const struct btf *local_btf, const struct bpf_insn *insn, >> + const struct bpf_core_relo_res *res) >> +{ >> + __u8 class; >> + const struct btf_type *orig_t; >> + >> + class = BPF_CLASS(insn->code); >> + orig_t = btf_type_by_id(local_btf, res->orig_type_id); >> + >> + /* >> + * verifier has to see a load of a pointer as a 8-byte load, >> + * CO_RE should not screws up access, bpf_core_patch_insn modifies >> + * load's mem size from 8 bytes to 4 bytes in 32-bit arch, >> + * so we skip adjust mem size. >> + */ > > Nope, this is only for BPF UAPI context types like __sk_buff (right > now). fentry/fexit/raw_tp_btf programs traversing kernel types and > following pointers actually need this to work correctly. Don't do > this. Distinguishing BPF UAPI context from kernel type requires some work. According to current situation, the solution of patch2 is relatively simple.
Thanks, Yang
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