Messages in this thread | | | Subject | Re: [PATCH bpf RESEND 2/4] bpf: Remove size check for sk in bpf_skb_is_valid_access for 32-bit architecture | From | Yang Jihong <> | Date | Mon, 7 Nov 2022 17:12:10 +0800 |
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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
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