On Fri, Nov 4, 2022 at 2:56 PM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Thu, Nov 3, 2022 at 1:36 AM Yang Jihong <yangjihong1@xxxxxxxxxx> wrote: > > > > The error code -EACCES is returned when bpf prog is tested in 32-bit environment, > > This is because bpf_object__relocate modifies the instruction to change memory > > size to 4 bytes, as shown in the following messages: > > > > libbpf: prog 'kfunc_call_test1': relo #2: matching candidate #0 <byte_off> [18342] struct __sk_buff.sk (0:30:0 @ offset 168) > > libbpf: prog 'kfunc_call_test1': relo #2: patched insn #1 (LDX/ST/STX) off 168 -> 168 > > libbpf: prog 'kfunc_call_test1': relo #2: patched insn #1 (LDX/ST/STX) mem_sz 8 -> 4 > > > > As a result, the bpf_skb_is_valid_access check fails. For 32-bit architecture, > > unnecessary checks need to be deleted. > > > > Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx> > > --- > > net/core/filter.c | 2 -- > > 1 file changed, 2 deletions(-) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index bb0136e7a8e4..eab7ce89740c 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -8269,8 +8269,6 @@ static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type > > return false; > > break; > > case offsetof(struct __sk_buff, sk): > > - if (type == BPF_WRITE || size != sizeof(__u64)) > > - return false; > > this probably should be specific to host architecture bitness? I'd > imagine that size = 4 should be invalid on 64-bit arches (reading half > of the pointer is bad) Not quite. In __sk_buff the field 'sk' is defined as: __bpf_md_ptr(struct bpf_sock *, sk); so it's always 64-bit load when bpf prog reads it. In this case CO_RE shouldn't have been applied to uapi struct __sk_buff.
