Hello,
On 2022/11/3 19:23, Russell King (Oracle) wrote:
On Thu, Nov 03, 2022 at 05:21:16PM +0800, Yang Jihong 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.
Isn't the purpose of this check to ensure that the entire pointer is
written, and BPF can't write half of it?
case offsetof(struct __sk_buff, sk):
- if (type == BPF_WRITE || size != sizeof(__u64))
- return false;
Wouldn't "(size != sizeof(struct bpf_sock *) && size != sizeof(__u64))"
be more appropriate here, so 32-bit can only write the 32-bit pointer
or the full 64-bit value, and 64-bit can only write the 64-bit pointer?
Or is there a reason not to? bpf folk?
Thanks for the detailed proposals, will fix it in next version.
Thanks,
Yang
